Baby on a trampoline

The act of pulling taught the scrotum in the "batwing" fashion and continuing to bounce one's flaccid small penis of said flap, thus creating the image of a baby jumping on a trampoline.

Hey....you ever seen a baby on a trampoline?
(pulls scrotum taught and bounces dingaling off it repeatedly) *everyone screams and gives a look of disgust...then they laugh.