ninja punch
The negative outcome of showing off.

The term originally came about from someone declaring that he was going to "ninja punch" another, but bent his wrist upon impact and ended up hurting himself more than the other person.
Ninja punch can apply to any action, not just a punch, in which the person doing the "ninja punch" is attempting to show off to others, and fails horribly.
While playing a role play game, Billy attempted to throw a grenade at the enemy by bouncing it off of three walls and down the hall. Sadly for Billy, and those standing next to him, he rolled a 1 (critical failure) and dropped the live grenade at his feet.
One of the other plays declared "Way ta ninja punch!"