A variation of the fart game. When your friend passes gas, and you say "Buck Six" before he has a chance to say "Safety", you get to slug them six times. If they say "Safety" right after they fart, then no slugs allowed.
Mark rips ass for a few seconds. Greg hears it from across the room and yells "Buck Six!". Mark tries to say "Safety" without shitting his pants while Greg slugs him six times in the arm.