Green’s Dictionary of Slang

butt adv.

[butt n.1 (1a), seen as something physically powerful]

(US campus) a general intensifier, very, very much, extremely, incredibly, truly.

[US]Eble Campus Sl. Oct. 2: butt – very, extremely: Yeah, she was butt ugly.
[US]P. Munro Sl. U. 51: I had to get up butt early this morning for my eight o’clock class.

In compounds

butt-crazy (adj.)

(US teen) utterly, completely insane.

Democrat & Chron. (Rochester, NY) 22 Feb. 7A/2: ‘I’ve only been here a matter of weeks and I’m going butt crazy’.
[US]A. Heckerling Clueless [film script] I am majorly, totally, butt-crazy in love with Josh.
butt-ugly (adj.) (also bugly, butt, buttly) [butt n.1 (1a) + SE ugly] (US)

1. very ugly.

Phila. Dly News (Phila., PA) 8 Dec. 79: [TV highlights] Hill takes on Vince ‘Butt Ugly’ Stafford on ‘Hill Street Blues’ (Channel 3 at 10).
(con. 1966–8) R. Zumbro Tank Sergeant 163: A dozen chickens pecked in the dust, while one of those butt-ugly Viet pigs foraged in the garbage heap.
[US]Eble Campus Sl. Oct. 2: butt – very, extremely: Yeah, she was butt ugly.
[US]P. Munro Sl. U. 52: That guy dancing with Julie is buttly.
[US]D. Burke Street Talk 2 15: He’s butt ugly! [...] She’s buttly!
[US]C. Hiaasen Stormy Weather 61: The other muggers piled out [...] with the intention of killing the butt-ugly geek.
[US]Eble Campus Sl. Apr. 2: butt – ugly.
[US]College Sl. Research Project (Cal. State Poly. Uni., Pomona) [Internet] Bugly (adj.) Butt ugly.
[US]Mad mag. Apr. 41: 2 out of 3 plastic surgeons admit that about 40% of their patients will remain ‘butt-ugly’ no matter how many facelifts [...] they get.
[UK]A. Wheatle Dirty South 6: Geoffrey always had lyrics but then he had to have lyrics. He was fat and butt ugly.

2. a general derog.

[US]T. Dorsey Florida Roadkill 237: The Hurricanes had a butt-ugly season this year.