diff --git a/r2/r2/controllers/api.py b/r2/r2/controllers/api.py
index 96183de44..87f8d5259 100644
--- a/r2/r2/controllers/api.py
+++ b/r2/r2/controllers/api.py
@@ -31,7 +31,7 @@ from r2.models import *
 from r2.lib.utils import get_title, sanitize_url, timeuntil, set_last_modified
 from r2.lib.utils import query_string, timefromnow, randstr
 from r2.lib.utils import timeago, tup, filter_links, levenshtein
-from r2.lib.pages import FriendList, ContributorList, ModList, \
+from r2.lib.pages import EnemyList, FriendList, ContributorList, ModList, \
     BannedList, BoringPage, FormPage, CssError, UploadedImage, \
     ClickGadget, UrlParser
 from r2.lib.utils.trial_utils import indict, end_trial, trial_info
@@ -184,7 +184,8 @@ class ApiController(RedditController):
         handles message composition under /message/compose.
         """
         if not (form.has_errors("to",  errors.USER_DOESNT_EXIST,
-                                errors.NO_USER, errors.SUBREDDIT_NOEXIST) or
+                                errors.NO_USER, errors.SUBREDDIT_NOEXIST,
+                                errors.USER_BLOCKED) or
                 form.has_errors("subject", errors.NO_SUBJECT) or
                 form.has_errors("text", errors.NO_TEXT, errors.TOO_LONG) or
                 form.has_errors("captcha", errors.BAD_CAPTCHA)):
@@ -492,7 +493,7 @@ class ApiController(RedditController):
                 nuser = VExistingUname('name'),
                 iuser = VByName('id'),
                 container = VByName('container'),
-                type = VOneOf('type', ('friend', 'moderator', 
+                type = VOneOf('type', ('friend', 'enemy', 'moderator', 
                                        'contributor', 'banned')))
     def POST_unfriend(self, nuser, iuser, container, type):
         """
@@ -517,7 +518,7 @@ class ApiController(RedditController):
             abort(403, 'forbidden')
         # if we are (strictly) unfriending, the container had better
         # be the current user.
-        if type == "friend" and container != c.user:
+        if type in ("friend", "enemy") and container != c.user:
             abort(403, 'forbidden')
         fn = getattr(container, 'remove_' + type)
         fn(victim)
@@ -528,8 +529,6 @@ class ApiController(RedditController):
         if type in ("moderator", "contributor"):
             Subreddit.special_reddits(victim, type, _update=True)
 
-
-
     @validatedForm(VUser(),
                    VModhash(),
                    ip = ValidIP(),
@@ -553,8 +552,8 @@ class ApiController(RedditController):
                  and not c.site.is_moderator(c.user))):
             abort(403,'forbidden')
 
-        # if we are (strictly) friending, the container had better
-        # be the current user.
+        # if we are (strictly) friending, the container
+        # had better be the current user.
         if type == "friend" and container != c.user:
             abort(403,'forbidden')
 
@@ -765,6 +764,36 @@ class ApiController(RedditController):
             return
         Report.new(c.user, thing)
 
+    @noresponse(VUser(), VModhash(),
+                thing=VByName('id'))
+    def POST_block(self, thing):
+        '''for blocking via inbox'''
+        if not thing:
+            return
+        # Users may only block someone who has
+        # actively harassed them (i.e., comment/link reply
+        # or PM). Check that 'thing' would have showed up in the
+        # user's inbox at some point
+        if isinstance(thing, Message):
+            if thing.to_id != c.user._id:
+                return
+        elif isinstance(thing, Comment):
+            parent_id = getattr(thing, 'parent_id', None)
+            link_id = thing.link_id
+            if parent_id:
+                parent_comment = Comment._byID(parent_id)
+                parent_author_id = parent_comment.author_id
+            else:
+                parent_link = Link._byID(link_id)
+                parent_author_id = parent_link.author_id
+            if parent_author_id != c.user._id:
+                return
+
+        block_acct = Account._byID(thing.author_id)
+        if block_acct.name in g.admins:
+            return
+        c.user.add_enemy(block_acct)
+
     @noresponse(VAdmin(), VModhash(),
                 thing = VByName('id'))
     def POST_indict(self, thing):
@@ -863,7 +892,8 @@ class ApiController(RedditController):
             not commentform.has_errors("parent",
                                        errors.DELETED_COMMENT,
                                        errors.DELETED_LINK,
-                                       errors.TOO_OLD)):
+                                       errors.TOO_OLD,
+                                       errors.USER_BLOCKED)):
 
             if is_message:
                 to = Account._byID(parent.author_id)
diff --git a/r2/r2/controllers/errors.py b/r2/r2/controllers/errors.py
index 84b0c4dd4..b718e25a2 100644
--- a/r2/r2/controllers/errors.py
+++ b/r2/r2/controllers/errors.py
@@ -32,6 +32,7 @@ error_list = dict((
         ('BAD_USERNAME', _('invalid user name')),
         ('USERNAME_TAKEN', _('that username is already taken')),
         ('USERNAME_TAKEN_DEL', _('that username is taken by a deleted account')),
+        ('USER_BLOCKED', _("you can't send to a user that you have blocked")),
         ('NO_THING_ID', _('id not specified')),
         ('NOT_AUTHOR', _("you can't do that")),
         ('DELETED_LINK', _('the link you are commenting on has been deleted')),
diff --git a/r2/r2/controllers/front.py b/r2/r2/controllers/front.py
index 2924119b5..7aa0bf827 100644
--- a/r2/r2/controllers/front.py
+++ b/r2/r2/controllers/front.py
@@ -897,6 +897,7 @@ class FormsController(RedditController):
             content = PaneStack()
             infotext = strings.friends % Friends.path
             content.append(FriendList())
+            content.append(EnemyList())
         elif location == 'update':
             content = PrefUpdate()
         elif location == 'feeds' and c.user.pref_private_feeds:
diff --git a/r2/r2/controllers/listingcontroller.py b/r2/r2/controllers/listingcontroller.py
index 325895313..1419571c7 100644
--- a/r2/r2/controllers/listingcontroller.py
+++ b/r2/r2/controllers/listingcontroller.py
@@ -625,6 +625,7 @@ class MessageController(ListingController):
     def keep_fn(self):
         def keep(item):
             wouldkeep = item.keep_item(item)
+
             # TODO: Consider a flag to disable this (and see above plus builder.py)
             if (item._deleted or item._spam) and not c.user_is_admin:
                 return False
diff --git a/r2/r2/controllers/validator/validator.py b/r2/r2/controllers/validator/validator.py
index e17ee088a..1fa28b4b9 100644
--- a/r2/r2/controllers/validator/validator.py
+++ b/r2/r2/controllers/validator/validator.py
@@ -711,11 +711,14 @@ class VSubmitParent(VByName):
         fullname = fullname or fullname2
         if fullname:
             parent = VByName.run(self, fullname)
-            if parent and parent._deleted:
-                if isinstance(parent, Link):
-                    self.set_error(errors.DELETED_LINK)
-                else:
-                    self.set_error(errors.DELETED_COMMENT)
+            if parent:
+                if c.user_is_loggedin and parent.author_id in c.user.enemies:
+                    self.set_error(errors.USER_BLOCKED)
+                if parent._deleted:
+                    if isinstance(parent, Link):
+                        self.set_error(errors.DELETED_LINK)
+                    else:
+                        self.set_error(errors.DELETED_COMMENT)
             if isinstance(parent, Message):
                 return parent
             else:
@@ -907,7 +910,11 @@ class VMessageRecipent(VExistingUname):
             except NotFound:
                 self.set_error(errors.SUBREDDIT_NOEXIST)
         else:
-            return VExistingUname.run(self, name)
+            account = VExistingUname.run(self, name)
+            if account._id in c.user.enemies:
+                self.set_error(errors.USER_BLOCKED)
+            else:
+                return account
 
 class VUserWithEmail(VExistingUname):
     def run(self, name):
diff --git a/r2/r2/lib/pages/pages.py b/r2/r2/lib/pages/pages.py
index c1cf37caf..64a14743e 100644
--- a/r2/r2/lib/pages/pages.py
+++ b/r2/r2/lib/pages/pages.py
@@ -2283,8 +2283,11 @@ class UserList(Templated):
     remove_action  = "unfriend"
     editable_fn    = None
 
-    def __init__(self, editable = True):
+    def __init__(self, editable=True, addable=None):
         self.editable = editable
+        if addable is None:
+            addable = editable
+        self.addable = addable
         Templated.__init__(self)
 
     def user_row(self, user):
@@ -2351,10 +2354,27 @@ class FriendList(UserList):
             return UserTableItem(user, self.type, self.cells, self.container_name,
                                  True, self.remove_action, rel)
 
+
+class EnemyList(UserList):
+    """Blacklist on /pref/friends"""
+    type = 'enemy'
+    cells = ('user', 'remove')
+    
+    def __init__(self, editable=True, addable=False):
+        UserList.__init__(self, editable, addable)
+
+    @property
+    def table_title(self):
+        return _('blocked users')
+
+    def user_ids(self):
+        return c.user.enemies
+
     @property
     def container_name(self):
         return c.user._fullname
 
+
 class ContributorList(UserList):
     """Contributor list on a restricted/private reddit."""
     type = 'contributor'
diff --git a/r2/r2/models/account.py b/r2/r2/models/account.py
index ecd8842c8..1aee87bed 100644
--- a/r2/r2/models/account.py
+++ b/r2/r2/models/account.py
@@ -251,6 +251,10 @@ class Account(Thing):
     def friends(self):
         return self.friend_ids()
 
+    @property
+    def enemies(self):
+        return self.enemy_ids()
+
     # Used on the goldmember version of /prefs/friends
     @memoize('account.friend_rels')
     def friend_rels_cache(self):
@@ -313,6 +317,12 @@ class Account(Thing):
         for f in q:
             f._thing1.remove_friend(f._thing2)
 
+        q = Friend._query(Friend.c._thing2_id == self._id,
+                          Friend.c._name == 'enemy',
+                          eager_load=True)
+        for f in q:
+            f._thing1.remove_enemy(f._thing2)
+
     @property
     def subreddits(self):
         from subreddit import Subreddit
@@ -622,7 +632,8 @@ def register(name, password):
 
 class Friend(Relation(Account, Account)): pass
 
-Account.__bases__ += (UserRel('friend', Friend, disable_reverse_ids_fn = True),)
+Account.__bases__ += (UserRel('friend', Friend, disable_reverse_ids_fn=True),
+                      UserRel('enemy', Friend, disable_reverse_ids_fn=True))
 
 class DeletedUser(FakeAccount):
     @property
@@ -644,3 +655,12 @@ class DeletedUser(FakeAccount):
             pass
         else:
             object.__setattr__(self, attr, val)
+
+class BlockedUser(DeletedUser):
+    @property
+    def name(self):
+        return '[blocked]'
+
+    @property
+    def _deleted(self):
+        return False
diff --git a/r2/r2/models/link.py b/r2/r2/models/link.py
index aa855d59b..18ba4b4f6 100755
--- a/r2/r2/models/link.py
+++ b/r2/r2/models/link.py
@@ -24,7 +24,7 @@ from r2.lib.db.thing import Thing, Relation, NotFound, MultiRelation, \
 from r2.lib.db.operators import desc
 from r2.lib.utils import base_url, tup, domain, title_to_url, UrlParser
 from r2.lib.utils.trial_utils import trial_info
-from account import Account, DeletedUser
+from account import Account, DeletedUser, BlockedUser
 from subreddit import Subreddit
 from printable import Printable
 from r2.config import cache
@@ -620,7 +620,10 @@ class Comment(Thing, Printable):
 
         inbox_rel = None
         # only global admins can be message spammed.
-        if to and (not c._spam or to.name in g.admins):
+        # Don't send the message if the recipient has blocked
+        # the author
+        if to and ((not c._spam and author._id not in to.enemies)
+            or to.name in g.admins):
             orangered = (to.name != author.name)
             inbox_rel = Inbox._add(to, c, name, orangered=orangered)
 
@@ -756,10 +759,16 @@ class Comment(Thing, Printable):
 
 
             # don't collapse for admins, on profile pages, or if deleted
-            item.collapsed = ((item.score < min_score) and
-                             not (profilepage or
-                                  item.deleted or
-                                  user_is_admin))
+            item.collapsed = False
+            if ((item.score < min_score) and not (profilepage or
+                item.deleted or user_is_admin)):
+                item.collapsed = True
+                item.collapsed_reason = _("comment score below threshold")
+            if c.user_is_loggedin and item.author_id in c.user.enemies:
+                if "grayed" not in extra_css:
+                    extra_css += " grayed"
+                item.collapsed = True
+                item.collapsed_reason = _("blocked user")
 
             item.editted = getattr(item, "editted", False)
 
@@ -959,7 +968,9 @@ class Message(Thing, Printable):
             # if the current "to" is not a sr moderator,
             # they need to be notified
             if not sr_id or not sr.is_moderator(to):
-                orangered = (to.name != author.name)
+                # Don't notify on PMs from blocked users, either
+                orangered = (to.name != author.name and
+                             author._id not in to.enemies)
                 inbox_rel.append(Inbox._add(to, m, 'inbox',
                                             orangered=orangered))
             # find the message originator
@@ -1090,6 +1101,13 @@ class Message(Thing, Printable):
                     item.is_collapsed = item.author_collapse
                 if c.user.pref_collapse_read_messages:
                     item.is_collapsed = (item.is_collapsed is not False)
+            if item.author_id in c.user.enemies:
+                item.is_collapsed = True
+                if not c.user_is_admin:
+                    item.author = BlockedUser()
+                    item.subject = _('[blocked]')
+                    item.body = _('[blocked]')
+
 
         # Run this last
         Printable.add_props(user, wrapped)
diff --git a/r2/r2/templates/comment.html b/r2/r2/templates/comment.html
index 4d47ec47a..5f0654b0d 100644
--- a/r2/r2/templates/comment.html
+++ b/r2/r2/templates/comment.html
@@ -91,7 +91,7 @@ ${parent.collapsed()}
   %endif
 
   %if collapse and thing.collapsed and show:
-    ${_("comment score below threshold")}
+    ${thing.collapsed_reason}
   %else:
     %if show:
        ${unsafe(self.score(thing, likes = thing.likes))}&#32;
diff --git a/r2/r2/templates/messagecompose.compact b/r2/r2/templates/messagecompose.compact
index 4e4601f2e..e0c8ac17a 100644
--- a/r2/r2/templates/messagecompose.compact
+++ b/r2/r2/templates/messagecompose.compact
@@ -39,6 +39,7 @@
     ${error_field("NO_USER", "to")}
     ${error_field("USER_DOESNT_EXIST", "to")}
     ${error_field("SUBREDDIT_NOEXIST", "to")}
+    ${error_field("USER_BLOCKED", "to")}
   </%utils:round_field>
 
   <%utils:round_field title="${_('subject')}">
diff --git a/r2/r2/templates/messagecompose.html b/r2/r2/templates/messagecompose.html
index 980a516a8..16969037d 100644
--- a/r2/r2/templates/messagecompose.html
+++ b/r2/r2/templates/messagecompose.html
@@ -55,6 +55,7 @@ function admincheck(elem) {
     ${error_field("NO_USER", "to")}
     ${error_field("USER_DOESNT_EXIST", "to")}
     ${error_field("SUBREDDIT_NOEXIST", "to")}
+    ${error_field("USER_BLOCKED", "to")}
   </%utils:round_field>
 </div>
 
diff --git a/r2/r2/templates/printablebuttons.html b/r2/r2/templates/printablebuttons.html
index 76b0a577d..fb880bb7b 100644
--- a/r2/r2/templates/printablebuttons.html
+++ b/r2/r2/templates/printablebuttons.html
@@ -302,6 +302,11 @@
   %endif
   %if thing.recipient:
     ${self.banbuttons()}
+      %if thing.thing.author_id != c.user._id and thing.thing.author_id not in c.user.enemies:
+        <li>
+          ${ynbutton(_("block user"), _("blocked"), "block", "hide_thing")}
+        </li>
+      %endif
     <li class="unread">
      ${self.state_button("unread", _("mark unread"), \
         "return change_state(this, 'unread_message', unread_thing, true);", \
diff --git a/r2/r2/templates/userlist.html b/r2/r2/templates/userlist.html
index e53837470..b3e83005d 100644
--- a/r2/r2/templates/userlist.html
+++ b/r2/r2/templates/userlist.html
@@ -23,7 +23,7 @@
 <%namespace file="utils.html" import="error_field"/>
 <% from r2.lib.template_helpers import static %>
 <div class="${thing._class} usertable">
-  %if thing.editable:
+  %if thing.addable:
     <form action="/post/${thing.destination}"
           method="post" class="pretty-form medium-text"
           onsubmit="return post_form(this, '${thing.destination}');"
diff --git a/r2/r2/templates/usertext.compact b/r2/r2/templates/usertext.compact
index 72c030194..eb6f571c0 100644
--- a/r2/r2/templates/usertext.compact
+++ b/r2/r2/templates/usertext.compact
@@ -83,6 +83,7 @@
         ${error_field("NO_TEXT", thing.name, "span")}
         ${error_field("DELETED_COMMENT", "parent", "span")}
         ${error_field("DELETED_LINK", "parent", "span")}
+        ${error_field("USER_BLOCKED", "parent", "span")}
         <a href="#" class="help-toggle button secondary_button">help</a>
       </div>
       <div class="markhelp-parent">
diff --git a/r2/r2/templates/usertext.html b/r2/r2/templates/usertext.html
index aad28b467..0bf22bf3d 100644
--- a/r2/r2/templates/usertext.html
+++ b/r2/r2/templates/usertext.html
@@ -79,6 +79,7 @@
         ${error_field("TOO_OLD", "parent", "span")}
         ${error_field("DELETED_COMMENT", "parent", "span")}
         ${error_field("DELETED_LINK", "parent", "span")}
+        ${error_field("USER_BLOCKED", "parent", "span")}
         <div class="usertext-buttons">
           ${action_button("save", "submit", "",
                           thing.creating and thing.have_form)}
diff --git a/r2/r2/templates/wrappeduser.html b/r2/r2/templates/wrappeduser.html
index 2026df85a..618b3edf6 100644
--- a/r2/r2/templates/wrappeduser.html
+++ b/r2/r2/templates/wrappeduser.html
@@ -27,6 +27,8 @@
 %else:
   %if thing.user_deleted:
     <span>[deleted]</span>
+  %elif thing.name == '[blocked]':
+    <span>${_(thing.name)}</span>
   %else:
     ${plain_link(thing.name + thing.karma, "/user/%s" % thing.name,
                _class = thing.author_cls + (" id-%s" % thing.fullname),