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1.
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!
That dude is so butt-ugly that just the sight of him makes me wanna puke!
by Victor Felix August 21, 2005
 
2.
very ugly
(from butt=very)
This room is butt ugly.
by Light Joker March 21, 2004
 
3.
As ugly as buttocks. Mostly like large, hairy and deformed buttocks.

(Not Jennifer Lopez's buttocks)
That bitch is butt ugly
 
4.
Exceedingly ugly. Originated by GIs in WWII, this term is as fresh as ever.
He came in butt ugly after a night of hard partying
by Bill Peters November 09, 2006
 
5.
A condition of being extremely ugly.
That dog is butt-ugly.
by Duckbutt May 26, 2006
 
6.
A person or object deemed so ugly (unattractive physically) they had to add butt in front of it.
Damn, did u see that girl Ashleigh? She is butt ugly!!
by DubbinMau5 September 09, 2010