The Goatse Convention:
When a link or picture involving the Goatse Man is brought into the discussion, the discussion is probably over, and the person who brought up the Goatse Man is probably a troll.
"The Goatse Man", goatse, or goatse.cx is an infamous photograph of a man with his hands grotesquely stretching his anus, bending over with his rear facing the camera.
