Gibbering Mouther: These pathetic, yet savagely dangerous creatures stalk conventions looking for unsuspecting victims they can attach themselves to. Anyone who pays them attention rapidly becomes their prey, as they latch onto the poor soul and begin an endless, one-sided conversation about the Mouther's personal geek-related obsession (which can be anything from his brilliant Magic deck to his theories on what the writers of Lost are really thinking to the super-cool character he made for Dungeons and Dragons that only bends the rules a little but is sooo bad-ass.) Once a Gibbering Mouther attaches itself to a fan, it can take hours to successfully extricate oneself--if indeed you can. Convention staff find upwards of twenty dead bodies every year after every con, gruesome victims of Gibbering Mouthers with gaping holes in the back of their heads where the poor fool's brain force-evolved teeth and chewed its way out through its own skull to escape the conversation.
But the worst thing about Gibbering Mouthers isn't the horrible, debilitating effect they have on their prey. The worst thing is that due to the symptoms--total obliviousness to one's own dullness, a tendency to assume everyone is interested in everything you have to say, and a blanket assumption that failure to shout, "SHUT UP!" at you and run away means that you should continue talking--you may already be a Gibbering Mouther and not even know it.