Green’s Dictionary of Slang

1. mad, very foolish.

1887		Lantern (N.O.) 9 Apr. 3: Humor him as he was a little off.
1902		Ade Girl Proposition 30: Dora tells him that he is Off.
1925		F.R. Pierce ‘Butler’s Nag’ in Goodstone Pulps (1970) 73/1: He’s a little off upstairs.
1936		J. Curtis Gilt Kid 48: Calling for two large brandies in one glass sounded a bit off, if you asked her.
1940		E.F. Frazier Negro Youth 180: ‘After all, a colored person who says he doesn’t want to be white must be kinda off’.
1959		(con. 1940s) E. Lambert Glory Thrown In (1961) 13: ‘Politics are for conformists, and crooks, and time-servers.’ ‘He’s off!’ announced Horrible John.
1960		H. Pinter Caretaker Act III: You’re up the creek! You’re half off!
1972		C. Fuller Jr ‘Love Song for Wing’ in King Black Short Story Anthol. (1972) 144: All those Robinsons act a little off.
1998		(con. 1986) G. Pelecanos Sweet Forever 31: He must have been off to think that a new record store could go down here in Shaw.
2008		W.D. Myers Game 35: I didn’t mess with him too tough because the dude acted like he might have been a little off.

2. happy, elated, enjoying the positive effects of drugs or drink.

1970		D. Mitchell Thumb Tripping (1971) 95: Wow, Gary! you’re sure off now, aren’t you? You’re somewhere else!
1992		Eble Campus Sl. Apr. 7: off – wild, carefree: ‘After two drinks, she was off’.

3. (US) hungover.

1882

Buffalo Wkly Exp. (NY) 4 May 1/5: Looks as if I’d been out on a tear last night [...] don’t I?’ ‘No [...] Just a little “off”’.