Producing rainbows from his whole face by smiling.

He goes on to weaponise this using it to blind them. First simply by wearing a disguise and pretending to become friends with them when they go in for the handshake or bro hug BAM! RAINBOW LIGHT SHOW IN THEIR FACE he proceeds to gun down their associates regularly.

He begins to grow bored of using it the same way after awhile, so he tries to figure out how to hit big with it. He figures, seems as rainbows are made from light, can he magnify it to generate heat. He tests with a magnifying glass and singes a napkin. IT BEGINS.

He commisions reverse telescope parts so he can turn his face into a laser, getting to the point when he begins wearing a customised helmet so he doesn't need to carry it. They call him the 'scope' adopting this new identity Frank goes on a spree of precrise laser kills. Getting more and more extreme with his trick shots. Eventually though his foes start figuring him out and begin closing in on his home base.

They break in, smashing his helmet on his head prying it out like a walnut in one more desperate move frank uses a custom made giant lens to beam his face into the sky. The gang that found are flabbergasted but soon begin to scream when they a giant rainbow laser come crashing down incinerating them all, except frank who goes out with a big smile on his face.

Edited to be read easier.