a sexual act. performed while giving fellatio or hand job, where as the giver uses their palm (well lubricated to avoid this being painful and causing friction burn) and very quickly rubs the head of the penis much like rubbing a clitoris. . .
this is called a "stormtrooper" because you are "polishing the helmet".
in the middle of giving him head, i stormtroopered him and he came all over!