n. a game in which the players attempt to catch each other by surprise by utilizing the back of the hand to strike each other in the scrotum.
Official rules of the game require players to verbalize the word "slapnutz" before making physical contact with other player's scrotum thereby giving notice, albeit short, of the intent to strike.
Often played at parties or other social gatherings and is especially embarrassing when played in the company a young lady that one of the players is attempting to tap.
Mark tagged in to the game of slapnutz, so his junk is fair game. He is such a tool bag.