Sweet anal sex of sexiness.
(can also be used as a verb, meaning "to buttfuck")
Bro 1: "Hey man, did you chumna Michelle last night? She's been walking funny all day!"
Bro 2: "Yeah bro, I chumna'd her sooo hard. She wont ever walk in a straight line again!"
Bro 1: "BROFIST!"
Bro: "Have you ever had chumna before, babe?"
Babe: "No, but I heard it smells awful."