Green’s Dictionary of Slang

1. the vagina.

1658		‘Erotodidascalus’ Rare Verities 4: Stone are by use made soft, irons wore to dross; / That never wears, and therefore feels no loss.
1793		Bacchanalian Mag. 41: Of a fam’d Monosyllable, doubtless, you’ve heard, / [...] / But, tho’ numerous names it is call’by, ’tis flat, / That the prop’rest of all is no other than That.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 57: Ce. The female pudendum; ‘that.’.

2. sexual intercourse.

1685–88		‘A New Dialogue’ in Ebsworth Bagford Ballads (1878) I 70: A fulsome Trot, and good for naught, / unless it be for that.
1883		‘Three Chums’ in Boudoir I 6: Oh, those two boys are dreadful, just as if they would want any more of ‘that’ when they got home.
1958		(con. 1940s) B. Behan Borstal Boy 350: Charlie seldom joined in talk about that.

3. the penis.

[a.1556		in H. Rawson Dict. of Invective (1991) 109: Pietro Aretino (1492–1556) [...] wrote a series of dialogues ... ‘Speak plainly and say “fuck,” “prick,” “cunt,” and “ass” if you want anyone except the scholars at the university in Rome to understand you. You with your “rope in the ring,” your “obelisk in the Colosseum,” . . . [...] not to mention your [...] “little monkey,” your “this,” your “that,” [...] and all shit there is.’].
1890–1904		Farmer & Henley Sl. and Its Analogues.