An alternator (noun) is a masturbator who can masturbate with either hand. Being an alternator can be very handy, so to speak, if you break your wrist, hand or your whole arm on your normally dominant side.
Using the other hand is also safer if you have a rash on your normally dominant hand. You wouldn’t want that rash to spread to your naughty bits, now would you?
Some bible-thumping evangelists think that alternators will be twice-roasted in hell. Other people—not all of them deeply religious—think that alternators will grow hair on both palms. There is no known scientific evidence that either supports or refutes these hypotheses.