Green’s Dictionary of Slang

1. a euph. depending on context; if sexual, ref. to the vagina or penis; if hostile, the anus or the testicles.

1723		Rape of the Bride 14: Next Moles [...] / That by your Lips, with Tuft of hair, / Shews you’ve another — you know where.
1768		Gentleman’s Bottle-Companion 7: Like diapalma-plaister roll’d, / He placed it you know where, Sir.
1787		Harris’s List of Covent-Garden Ladies 85: Oft shall her hand / Your — command, / And put it you know where.
1834		‘The Rising Generation’ in Randy Songster in Spedding & Watt (eds) I 199: She puts her hand on — you know where, / And longs for the rising generation!
1838		Crim.-Con. Gaz. 22 Sept. 35/3: She damned me [...] / She bad me kiss her — you know where.
1884		Kryptadia II in G. Legman (1968) 344: His you-know-what was you-know-where; / If that wasn’t fucking, then I wasn’t there.
1952		J. Cleary Sundowners 13: Don’t let me catch you looking at any flappers. Or [...] I’ll kick you in the you-know-where.
1962		C. Clausen I Love You Honey, But the Season’s Over 20: Kee-rist! I’ve got a rope burn from my ankle up to you-know-where.
1974		(con. 1945) M. Angelou Gather Together In My Name 91: Now, take that filthy pattern and stick it you-know-where.
1984		‘Derek Raymond’ He Died with His Eyes Open 56: Since I was in the cats meat gaff [...] for my piles, I find walkin any distance brings a pain on you know where.
1999		Ian Dury ‘Mash It Up Harry’ 🎵 And he wants a bit of Wembley up his you-know-where.
2023		(con. 1962) J. Ellroy Enchanters 50: [F]oster daddies who poked us you know where when we were eight.

2. hell.

[1855		‘Sunday Trading Bill’ in C. Hindley Curiosities of Street Lit. (1871) 115: He ought to be kicked to I know where].
1979		‘Iceberg Slim’ Airtight Willie and Me 75: I hoboed heroin’s express train to you know where.

3. (also where you know) the lavatory.

1922		Joyce Ulysses 338: When she wanted to go where you know she said she wanted to run and pay a visit to Miss White.
1960		G.W. Target Teachers (1962) 188: Who should be the first goon I trip over coming in [...] but this batty-looking old dear tottering out of the you-know-where.