Green’s Dictionary of Slang

bareback adv.

[the nakedness of the penis; note ride v. (1a)]

having sexual intercourse without using a contraceptive sheath; also occas. as adj.; thus bareback rider, a man who has sex without a condom.

[US]M. Richler Apprenticeship of Duddy Kravitz (1964) 185: You’re twenty-four years old. Don’t you know better than to go bareback?
[US]Wentworth & Flexner DAS 20/1: bareback rider A male who enters into sexual intercourse without using a contraceptive.
[US]M. Puzo Godfather 313: I’ve had to treat him three times for clap and once for syphilis. Freddie is the original bareback rider.
[US]B. Rodgers Queens’ Vernacular 97: go Hollywood (obs, ’40s) 1. to mingle with gays . . . socially or bareback.
[US](con. 1945) M. Angelou Gather Together In My Name 165: He opened his pants. Dignity rode his face bareback.
[US]S. King It (1987) 518: Your days of gaily going in bareback with no questions asked have temporarily come to an end.
[US]in POZ June [Internet] Fucking raw. Riding bareback. Skin-to-skin. With such delicious images, it’s easy to stop thinking of it as unsafe sex.
[UK](con. 1981) A. Wheatle East of Acre Lane 253: Charge more fe a bareback rider, £5 more.
[UK](con. 1981) W. Self Dorian 115: I’ve heard that you keep right on doing all kinds of stuff, riding bareback —.
Treasure Island Media video catalogue [Internet] Knocked Up [...] KNOCKED UP features a whole congregation of the hottest big-dicked topmen I know. Steve Parker, Titpig, Tom Shannon, Erich Lange (in his video debut as a bareback top) [...] and a bunch of other testosterone-driven men with nothing on their minds but fuck-or-be-fucked.
[UK]D. Seabrook Jack of Jumps (2007) 189: And yet at least one man got to ride Teddy bareback.
[US] 20 Nov. [Internet] Big-screen, high-definition televisions displayed [...] bareback bear porn on four walls.
[UK]I. Welsh Decent Ride 33: So ah’m thinkin aboot lassies '[...] ah fired intae bareback that weekend. 9 Nov. [Internet] California votes against banning bareback porn.

In derivatives

barebacking (n.) (also bareback riding)

hetero- or homosexual intercourse without the use of a condom.

[US]R. Scott Rebecca’s Dict. of Queer Sl. [Internet] barebacking or bareback sex — unsafe sex. A term used mostly by gay men.
[UK]Guardian 27 Jan. 22: What Peter Mandelson did was the political equivalent of bare-backing [...] episodes of unprotected sex.
OnLine Dict. of Playground Sl. [Internet] bareback riding v. to have sexual intercourse (homo. or hetero.) without using a condom.