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.
(..) Be careful. What's that smell? Some teenagers probably just broke in here, to drink beer, and bump uglies. Exactly. Mom would've hated seeing the cabin like this. Okay. Let's make this place livable. (..)2013 Evil Dead