Green’s Dictionary of Slang

1. a synon. for ‘you must be joking’ or ‘who do you think you’re fooling?’.

1959		B. Kops Hamlet of Stepney Green II ii: bessie: Davey – your sister’s on the line – come and say hello. david: Oh – do me a favour.
1966		B. Reckord Skyvers I ii: Wimmen! Do me a favour!
1978		P. Theroux Picture Palace 303: Boring? You have no idea. I used to look at Europe and think, Do me a favour!
1982		P. Theroux London Embassy 114: Do me a favour!
1995		J. Cameron Vinnie Got Blown Away 109: Scuse me guv, you interested nice second-hand VDU for her indoors? Do me a favour.
2005		M.B. ‘Chopper’ Read Chopper 4 21: Do me a very large favour, please.
2010		K. Richards Life 384: As far as that’s English law, I respect it very much. But do me a favor.

2. a phr. meaning stop harassing me, go away, be off.

1958		F. Norman in Sun. Graphic 20 July in Norman’s London (1969) 19: ‘Do me a favour!’ I replied and had it away a bit lively.
1972		B. Rodgers Queens’ Vernacular 66: do me a favor (interj, Brit gay sl, ’60s) keep quiet!
1983		A. Payne ‘Get Daley!’ Minder [TV script] 17: Do me a favour.
1996		J. Cameron It Was An Accident 4: Leave it out George I mean do me a favour.