Adj. used to describe the outward manifestation of negative attributes or anti-social beliefs.
Worker 1: It's not that she's unattractive, it's just that she's "ugly on the inside" and that shows on her face.
Worker 2: well, she's an HR hussy, they are ALL ugly on the inside.
Voter 1: it's weird, he looks good in photos but in real life you can see he's "ugly on the inside".
Voter 2: total hater, seriously. he's so racist and sexist what do you expect? he's ugly on the inside.