A game similar to conkers that involves two men and their genitalia.
Each man takes it in turn to whack the opponents balls with their penis. The receiver must ensure that their penis is held firmly up and out of the firing line so as not to interfear with a clean whack. This is repeated until the lesser man concedes defeat and the dispute is settled.
"Man i think your girlfriends hot; I'll give you a game of plonkers for her"