punching the munchkin
To simply put it,Masturbating. Applies only to men.
Bubba was caught in the closet punching the munchkin.
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.