black joke, n. — Green’s Dictionary of Slang

black joke n.

also coal black joke, joke

[contemporary popular song, first printed as ‘The original Black Joke’ (c.1720) and often linked to The Harlot Unmasked (c.1735); the chorus of both ran, ‘Her black joke and belly so white’; Williams dates Harlot to c.1707 (quoting Farmer Merry Songs) and notes that ‘the C18 saw numerous songs circulating to the tune ‘Black Joke’’; Partridge suggests ‘something to be cracked’]

the female genitals.

c.1720		‘The original Black Joke. Sent from Dublin’ 🎵 Her black joke and belly so white.
[1733		‘The Upper Gallery’ in A. Carpenter Verse in Eng. in 18C Ireland (1998) 246: Gay native Tunes assert our worthier Choice, / And the Black Joke resounds from ev’ry Voice.
c.1735		‘The Harlot Unmasked’ [song] Her black joke and belly so white.
1773		Harris’s List of Covent-Garden Ladies 102: A coal-black joke is here express’d.
1781		Belle’s Stratagem 66: I’d better be on the look out, that no one disturb you in your devotions [...] and whistle The Black Joke, there be any danger.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Black Joak a popular Tune with a Song having for its burthen ‘her Black Joak & Belly so white’ figuratively the black Joak resembles the Monosyllable.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Black Joke. A popular tune to a song, having for the burden, ‘Her black joke and belly so white:’ figuratively the black joke signifies the monosyllable.
1797		Sporting Mag. June X 176/1: Calls for a song [...] / ‘Hearts of Oak,’ ‘Britannia Rules the Main,’ ‘Roast Beef!’ ‘Black Joke’! or some such sort o’ thing.
1811		Lex. Balatronicum.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc.
1833		‘Hal And Cis’ in Regular Thing, And No Mistake 91: How pure a stroke ’twill be, nay fine, / When you clap your black joke to mine.
1834		‘A Vision!’ in Libertine’s Songster in Spedding & Watt (eds) I 138: She placed it [‘the gem’] somewhere in a joke / The deed extatic joy awoke.
1837		‘My Dear Black Joke’ in Flash Olio in Spedding & Watt (eds) Bawdy Songbooks (2011) III 210: My own black joke, my pretty black joke, / I own your power I love to provoke; / You joys, I know, man can’t forgo.
1842		‘The Long Three Square!’ in Nobby Songster 25: The jokes they are black as a kitchen coal, / Which all must admire when they look on the w-hole.
c.1850		Peeping Tom (London) 12 48/3: [advert] tuzzy muzzy songster — Lucy and Kitty’s Black Jokes.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1986–7		Maledicta IX 52: black joke n [L] Pudendum of a black woman.