When one man places his sack on another man's back. Used in the penis showing game
Wacko:(standing shirtless working out)I love working out
Ed: (standing naked)I love my sack on people's backs
(jumps on Wacko's back, and his sack is on Wacko's back, thus giving him sack back)
Wacko: God damn it Ed!
Ed: Gotchya Wacko!
(Proceeds to kick Wacko in the ass twice)