The act of vigorously whipping your dick back and forth (left and right) so that it makes contact with your legs. The resulting impact produces a smacking sound, and if done rapidly, it can sound like clapping.
Instead of clapping with his hands at the end of the show, George stood up, dropped his pants, and started penis clapping like a boss.
when two nude men stand facing one another and thrust their pelvises causing their penises to fly forward making contact and emitting a percussive sound.
Devendra Banhart was penis clapping with that drummer from his band.