Green’s Dictionary of Slang

1. (Aus./N.Z./UK) the anus, the backside as a whole.

1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: date. (1) A term for the posterior orifice.
1945		‘Cats on the Rooftops’ in Mess Songs & Rhymes of RAAF 1939-45 1: The Australian lady emu [...] / Wanders round the desert with a feather up her date .
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 79: I hear tell the French tarts don’t say no to robbing the occasional date locker.
1973		(con. 1940s–60s) Hogbotel & ffuckes ‘Tit Bits’ in Snatches and Lays 12: She wishes, no doubt, with a fervor devout, / That he’d bit not her tit, but her date. [Ibid.] ‘Cats on the Rooftops’ in Snatches and Lays 25: The Australian emu, when she wants to find a mate, / Wanders round the desert with a feather up her date.
1973		B.S. Johnson All Bull 63: Boy, the state o’ my date — honest, it’s like burnin’ rubber.
1989		R.G. Barrett Boys from Binjiwunyawunya 13: He’s shoving the pineapple right up my date.
1998		R.G. Barrett Goodoo Goodoo 40: I’d have riped that microphone out of the dash and shoved it fair up his date.
1999		G. Seal Lingo 88: The extent and variety of the Lingo terms for genitals and other body areas hints at a determined, if perverse, use of euphemism to avoid the use of perfectly respectable words like testicles, penis, vagina, and posterior. Such terms, though, seem sterile and colourless to the Lingoist who prefers such delights as [...] date, fanny, arse, bum dot, backside (spot your dot being an affectionate invitation to take a seat), blot, to name only a very, very few.
2002		R.G. Barrett Mystery Bay Blues 62: [He] shuffled around [...] like Marriane [sic] Faithfull with an axe handle stuck in her date.
2005		M.B. ‘Chopper’ Read Chopper 4 219: The good old Victoria Police Force has [...] bashed the barrel of a .38 calibre police special up the date of some scallywag.
2017		T. Spicer Good Girl Stripped Bare 106: We date (ew, sounds like a dried fruit or a bumhole).

2. (Aus.) a term of abuse [f. sense 1].

1919

W.H. Downing Digger Dialects 18: date — A word signifying contempt.