Green’s Dictionary of Slang

to answer back, to argue.

1896		‘Army Slang’ in Regiment 11 Apr. 31/2: A private who is argumentative [...] is a ‘barrack room lawyer’ [...] and who, if the caution ‘not to give old smash’ or ‘back chat’ remain unheeded, will probably spend the night in the guard room.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: back chat. [...] (2) To answer back.
1926		L. Esson Bride of Gospel Place 109: Smithy: You should have seen me mount the peter and back-chat the ziffs.
1939		J. Campbell Babe is Wise 211: ‘I’m gonner sleep somewhere else,’ she tells me, ’oity-toity.’ ‘Oh,’ I backchats, ‘w’ere?’.
1953		R. Mais Hills were Joyful Together (1966) 40: You see how my gal can back-chat me an’ get away with it?
1960		Atlantic CCVI 93: ‘Don’t back-chat me, you bloody thief!’ Mister Cockburn yell.
1993		Age (Melbourne) Good Weekend 6 Nov. 41/1: ‘[He] had his nose broken by his mum for backchatting’.
2004		N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 173: He [...] had lost almost three months of it, mostly for backchatting the screws.