A perjorative term for someone so ugly, so exceedingly unattractive. that he or she is as "ugly as a butt" (a misnomer, since many buttocks are beautiful indeed). A popular teen-age slang term since the 80s, "butt-ugly" most probably began as military slang c. World War II. Probably because enlisted men found nothing attractive about another enlisted man's hairy, sweaty, very possibly pimpled butt!
Example: That dude is so butt-ugly that just the sight of him makes me wanna puke!
A term used to describe an incredibly ugly person; someone you'd have to turn around to fuck. For people who aren't into anal, this is somewhat drastic.
Example: Robin: Dude, look at the chick! She's so butt-fucking ugly! Oliver: I dunno, man, I think I'd just paper bag her.
James: Hey, fuck off, dude! That's my sister!
Oliver: Family resemblance, eh?