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.
(..) - Are you crazy? One good coach for four years. The Celtics are like a dynasty! Come on, man. The Celtics were, like, the ugliest team in the history of sports. A dynasty of ugly motherfuckers, man. Look at Kevin McHale. James Worthy? The guy has a head like a melon. - No, he had ladies. (..)1998 American History X
(..) from Chino earlier this morning... ...after serving three and some-odd years. I think this is something we gotta keep an eye on. If something happens to him... ...things could get very ugly down by the beach. Just keep it low. DANNY: Venice Beach didn't always look like this. (..)1998 American History X