The art of jamming an entire fist into an orifice, usually a vagina or asshole. When performed correctly, the "fistblaster" should be elbow-deep in the "fistblastee". While inside the orifice the fist should be shaken in a dice rolling motion, but more violently, with the purpose of inducing orgasm and shaking out any loose change and/or any other objects such as a lost and forgotten tampon.
When I see Superman fly fist first, I always think he must be on his way to fistblast Lois Lane. That whore can really take a pounding.