as ugly as sin

(as) ugly as sin

Extremely visually displeasing or unattractive. This old car is all beat up and ugly as sin, but it's still going strong after all these years. I'm sure I looked as ugly as sin by that point, with my makeup smeared all over the place and my hair a total mess.
See also: sin, ugly
Farlex Dictionary of Idioms.

(as) ugly as sin

mod. very ugly. This car’s as ugly as sin, but it’s cheap and dependable.
See also: sin, ugly
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • (as) ugly as sin
  • ugly as sin
  • be (as) ugly as sin
  • (as) ugly as a toad
  • toad
  • ugly as a toad
  • pug-ugly
  • plug-ugly
  • fugly
  • fell out of the ugly tree and hit every branch on the way down