Also known as a Locker Room Cock (LRC)), a show-er is a penis that remains large and especially long when it isn't hard, the opposite of which is a grow-er, which shrinks to a much smaller size when sportin a softy.
A show-er is often the envy of the locker room and nude beach.
Jason: Damn, did you see that? That guy in the showers--his dick was huge!
Jack: Whatever. He's probably just a show-er.