nutsack slap Share definition Flag The art of being able to make a slapping sound by bouncing your nutsack off of your thighs due to humping the air back and forth. Dude! That nutsack slap was so loud, it woke the whole damn house! nutsack slap by wtfuwant January 23, 2011 0 0 Get merch Get the nutsack slap mug. Buy Now — $32.95 See more merch