Where you jab your hand up someone else's ass, but then, quickly forming your hand into a fist before it hits the anus. The resulting impact kills the person instantly. Ideal for a KO move.
Inspired by the term "anal death punch" and the band "Five Finger Death Punch" (an amalgamation of each phrase).
It's when someone has the sudden, unstoppable urge to violently punch in a non-sexual way usually leaving the receiver very harmed or at the very least traumatized.