When a
male is bored in the
shower and stretches his scrotum out and bounces his penis off of it so that looks like his penis is bouncing on a
trampoline.
Guy 1. "You know when you're bored in the
shower and you stretch your ballsack out and
bounce your dick off of it like it's bouncing on a trampoline?"
Guy 2. "What the fuck??? No...."
Guy 3. "Oh, you
mean playing the sack drum?"
Guy 1. "Yeah, exactly."