Fink

From the introduction: Fink is a game of social unpleasantness. It is about manipulative back-stabbing performed by "friends" upon supposed "friends". The core idea of the game is to be as nasty as possible to the people around you – both game-master controlled characters and those of fellow players – while preserving the illusion of amicability and common values. The characters ruin their fellows’ lives, but the players stay friendly with one another.