Usually refers to men. Especially men who don't pay much
attention to their looks, in terms of grooming, hair and clothes.
However when they put some
attention to it they look good.
Best example is Shaggy from
Scooby-Doo. He always looks frumpy, stained, unshaven, slump, but you always
get the feeling that when he needs to escort Daphne Blake to her gf wedding Shaggy after a shave and a nice getup will look good.