Infiltration of a website by retards; the process whereby a website's increasing popularity renders it useless.
Message boards and other pages relying on user interaction for content are gradually overwhelmed by flame wars, online games are deserted but for those players using bots and sites where users rate films or games become an exercise in pointlessness as teenage boys trundle through giving zero or full marks apparently at random. The original audience will become sick of this and move on. Swift and rigorous action by moderators (see mod) can help to counter cretin creep but often is more trouble than it's worth. Also twat creep, ass creep.
Popbitch is a textbook example of twat creep.