Social suicide is a slang term used twice in Mean Girls. Social suicide is committing an act which kills one's social life. This is usually achieved by participation in something perceived as embarrassing. Both Regina George and Damian Leigh referred to this when hearing that Cady Heron might join the Mathletes.
In Mean Girls: Return of the Plastics, a game mode with the same name consists of the player receiving 1000 of popularity and 30 waves, unfortunately, defeating a Plastic gives nothing. It is recommended to play as Cady Heron during this game mode, as the Plastics defeated near her gives the player more popularity.