"Hundred Hand Fap" is the combination to two know phrases. "Hunder Hand" comes from a Godly game called Street Fighter 2, a character named E. Honda would use a move called the Hundred Hand Slap. The last part of the phrase "Fap" i guess come from the internet somewhere. Fapping is the sound effect a male would make when he masturbates, Strokes his Wii(beats his meat)

A casual invitation / threat used by an individual that is not afraid of fucking someone up.