Punch the munchkin
A euphemism to describe masturbation; knuckle shuffle on the piss pump; pounding the purple headed yogurt slinger; working the wand etc.
In anticipation of his first date with the hot chick in his class, Joe decided to punch the munchkin before heading out.
punching the munchkin
To simply put it,Masturbating. Applies only to men.
Bubba was caught in the closet punching the munchkin.