A slightly macabre but energizing exercise.
Players stand in a circle. One by one, each player steps into the center, shouts 'Massacre!' and kills all other players in a specific way they've invented (e.g. hand grenade, laser eyes, killer bees).
All 'killed' players die dramatically. Then the next player steps up with their own method. Speed is the point — deaths should be quick, creative, and over-the-top.