Green’s Dictionary of Slang

bring off v.

[DSUE suggests ‘probably since 16C’ (as he does for bring on under bring v.) but offers no citation or further proof; nor is there any ref. in a dict. (sl. or SE) before his own although HDAS offers a 1675 citation]

to bring to orgasm; thus in phrs. below.

[UK] T. Duffett Mock-Tempest III i: My Lord Bacchus leads ’em on; my Lady Venus brings ’em off.
[UK]C. Pearl in Blatchford Memoirs (1983) 56: The pleasure of bringing him off had brought me to a pitch of eagerness almost matching his own.
[US]Trimble 5000 Adult Sex Words and Phrases.
[US]J. Sayles Union Dues (1978) 186: She figured she’d play it open-and-shut, bring him off and charge him twenty for a fifteen-dollar straight.
[US]Maledicta IV:2 (Winter) 184: The common man is apparently still ignorant of the basic mechanisms involved in bringing off a woman, and still believes in an exclusively vaginal orgasm.
[UK]A. Hollinghurst Swimming-Pool Library (1998) 165: To the lav, where we brought each other off swiftly and greedily.
[UK]Roger’s Profanisaurus 3 in Viz 98 Oct. 6: bring off v. To cause to have an orgasm.
[UK]M. Dibdin Thanksgiving 61: The younger ones I can bring off in less than a minute. Older guys like you take longer.

In phrases

bring off by hand (v.) (also bring down by hand)

to masturbate (someone else).

[US]H.N. Cary Sl. of Venery I 122: To bring down (or off) by hand – To masturbate.
Kortpeel ‘A Good Marriage Apart From Sex’ on Eunuch.org 🌐 ‘Why not let me try to do something for you?’ ‘No you leave me alone.’ She visibly shuddered at the idea of me bringing her off by hand.
bring oneself off (v.)

to masturbate.

[US]A. Mathew ‘Lessons of Seduction III’ on Nifty Erotic Stories Archive 🌐 She started stroking there first lightly stroking, then faster and harder and deeper, then lightly again, and slowly again, changing the speed and the tempo and the force – that’s how I bring myself off, thinking about Suki reciprocating her.
[UK]J. Meades Empty Wigs (t/s) 891: Barry bringing himself off [...] with other hand trying to stop that woolly hairpiece slipping over his eyes.