Hmm, I thought a mullet was a star in heraldry, or a fish, so I looke it up. It is indeed both, the recent (1996, apparently) usage for the haircut may come from a 19th century pejorative term "mullet-head" (apparently derived from the shape of the fish) meaning a stupid person. Or maybe not, etymology not being an exact science. I wonder if I like mullet-rock? Or a fish called rock mullet?