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.
(..) Who's in charge here? Got any officers here? Got somethin' to say down here? - You an officer. Huh? - Fuck you. Fuck you. You're too fuckin' ugly to be an fuckin' officer. Who's the officer in charge? Huh? You in charge here? I am! I am! Boy, that was stupid. (..)1997 G.I. Jane