The act of vigorously whipping your dickback 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.
Synthetic clapping is the sound of clapping hands made by a synthesizer or through a software program like Synth-Werk rather than being made by a person clapping his or her own hands.