miserable/ugly as sin

(as) miserable as sin

Extremely unhappy, depressed, or wretched. Everyone just stood around looking miserable as sin during the ceremony. I felt as miserable as sin because of the breakup, but I was going to be best man at my brother's wedding, so I had to pick myself up and dust myself off.
See also: miserable, 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.

*ugly as sin

Cliché extremely ugly. (*Also: as ~.) Why would anyone want to buy that dress? It's as ugly as sin! Harold is ugly as sin, but his personality is very charming.
See also: sin, ugly
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

ugly as sin

Physically or morally hideous, as in I can't think why she likes that dog; it's ugly as sin. This simile, first recorded in 1801, replaced the earlier ugly as the devil.
See also: sin, ugly
The American Heritage® Dictionary of Idioms by Christine Ammer.

ugly as sin

If someone or something is as ugly as sin, they are very ugly. Even his kids were ugly as sin.
See also: sin, ugly
Collins COBUILD Idioms Dictionary, 3rd ed.

(as) miserable/ugly as ˈsin

(spoken) used to emphasize that somebody is very unhappy or ugly: He arrived at the party looking as miserable as sin. Some babies are as ugly as sin at that age.
See also: miserable, sin, ugly
Farlex Partner Idioms Dictionary

ugly as sin

verb
See as ugly as sin
See also: sin, ugly
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions

ugly as sin

Hideous, either physically or spiritually. This simile appears to have replaced the earlier ugly as the devil, mentioned by Daniel Defoe in his History of the Devil (1726). The first appearance in print was in Maria Edgeworth’s Popular Tales of 1804: “Why, she is ugly as sin!”
See also: sin, ugly
The Dictionary of Clichés by Christine Ammer
See also:
  • (as) miserable as sin
  • miserable
  • fall into sin
  • as sin
  • sin
  • mulligrubs
  • mullygrubs
  • have the mulligrubs
  • have the mullygrubs
  • ugly