It would either be Light Light Fruit, or Flash Flash Fruit, not sure how it would be said in japanese (hence not sure if hikari is accurate enough); the power to emit light from one's body.
Nothing would say F-U more than someone going to block your punch, only to be blinded by a huge flash of light from your fist. The light could also be concentrated when emitted, emulating the ability to shoot "laser beams". Also like a light bulb, the flesh of the user would heat up with any light being emitted.
And it doubles as entertainment too, neon sign right on the user's body!
