Green’s Dictionary of Slang

cauliflower n.3

[ult. cauliflower n.2 (1)]

1. the vagina.

[UK]Grose Classical Dict. of the Vulgar Tongue n.p.: Cauliflower [...] the private parts of a woman; the reason for this appelation is given in the following story. A woman, who was giving evidence in a case wherein it was necessary to express those parts, made use of the term cauliflower, for which the judge on the bench, a peevish old fellow, reproved her, saying she might as well call it an artichoke. Not so, my lord, replied she, for an artichoke has a bottom, but a **** and a cauliflower have none.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[Aus]Satirist & Sporting Chron. (Sydney) 4 Mar. 3/2: ‘The handsomest Flower,’ said at lady at the Floral Show [...] ‘is that ere Cauliflower.’ — The largest Cucumber, we understand, was that exhibited by the French Chevalier — ’twas a rum-un indeed.
[UK]Farmer & Henley Sl. and Its Analogues.
[US] in Randolph & Legman Ozark Folksongs and Folklore (1992) I 123: Cabbages an’ califlooer, it’s the wind that blows the grass, / Many’s the penny I have earned with the hole next to my arse.

2. sexual intercourse.

[US]D. Lypchuk ‘A dirty little story’ in eye mag. 8 July [Internet] ‘Hey, I’m all in a lather, in a season,’ he told her. ‘How’s about a bit of your father? I wouldn’t mind some cauliflower.’.

In phrases

do a bit of cauliflower (v.) (also eat cauliflower)

to have sexual intercourse.

[UK]Farmer & Henley Sl. and Its Analogues.
[US]A. Wallace ‘The Listress’ Salon.com 16 May [Internet] What activity are the following euphemisms for? 1. Eat cauliflower. 2. Wind up the clock. 3. Drive home. 4. Have a Northwest Cocktail. 5. Introduce Charlie. 6. Parallel park. 7. Buzz the Brillo. 8. Make the chimney smoke. 9. Talk about Uganda. Answer: Have sex.
[UK]Roger’s Profanisaurus in Viz 87 Dec. n.p.: cauliflower euph. Sex. e.g. ‘I fancy doing a bit of cauliflower’. From 18th C. slang for vagina.