A character in Dungeons & Dragons games with a "Chaotic Evil" alignment, played poorly and to the detriment of the game, usually resulting in the deaths of the character and his allies.
(See also: Lawful Stupid)
Chaotic Stupid Player: I kill the girl.
Chaotic Stupid Player: Because I'm evil.
DM: Okay, you murder the little girl in front of everyone to show how totally badass and evil you are. The militia charge you down and kill you.