Green’s Dictionary of Slang

a popular toast, abbr. of to the best cunt in Christendom.

1650		News from the New-Exchange (1731) 18: This Lady plays as well at the Best as at the Beast.
[1660		Wandring Whore III 3: I will show thee [...] the best red-lip’t C — in Christendom].
1674		Duffett Mock Tempest III i: A health to the best.
1681		Radcliffe Ovid Travestie 18: To th’ top you fill’d a Glass, and drank to th’ best.
1696		Motteux (trans.) Gargantua and Pantagruel (1927) II Bk V [prol.] 491: Be cheery my lads; and if you are for me, take me off three or five bumpers of the best.
1793		Bacchanalian Mag. 36: Maria, precious black-ey’d maid / Pull’d up her coats and shift / [...] /‘’Tis this alone the men do mean, / When to the best they toast’.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 33: Battre le beurre = to copulate with vigour; ‘to get the best and plenty of it’.