Green’s Dictionary of Slang

have it off v.

to copulate.

1937		J. Worby Other Half 171: I get good dough. I had it off to-night for five pounds.
1959		F. Norman Fings II i: You must ’ave been ’aving it off with ol’ Perce for some time now.
1965		G. Melly Owning Up (1974) 59: One afternoon Godbolt was having it off with his girl-friend (the early puritanism had largely withered).
1970		T. Parker Frying-Pan 49: There’ll be a couple of queers having it off together.
1985		J. Morrison Share House Blues 67: ‘A bunch of Veterinary students say they are going to catch you and castrate you, if you don’t stop having it off with their girls’.
1986		R. Campbell In La-La Land We Trust (1999) 154: Some jerkoff wanting footage of his woman getting fucked and having it off with another woman.
1989		A. Higgins ‘The Bird I Fancied’ in Helsingør Station and Other Departures 144: ’E’s ’aven it orff wiv ’er, see.
1999		P. Temple Black Tide (2012) [ebook] You’re having it off with a wine waiter.
1999		Observer Mag. 30 May 16: Ooh, you don’t want to go with her, she’ll have it off with anyone.
2000		Indep. Rev. 18 Jan. 4: So what if they had it off behind a few church altars?