an 'ugly duckling' that has become a beautiful swan [=an ugly/unsuccessful person or thing that has become beautiful/successful]
('informal') That dog of yours is '(as) ugly as sin'. [=very ugly]
The house is an 'ugly duckling', but it has a lot of potential.
(..) There's a smelly Syrian just opened up downtown, babe. - I need three winners to get back. - Do you hear him? If I had three winners, would I be with an ugly junkie like this? - Gimme a winner, you germ. - Stop calling in a winner. The game ain't even started yet. How do you like this guy? (..)1974 The Gambler
(..) The manager came up to the room and told us we had to leave the hotel. And Eugene started bangin' on him, really bad... till these two big guys came up... ugly guys. One of them had this fresh purple scar on his neck. And he grabbed Eugene from behind... and the other guy (..)1974 The Gambler