Green’s Dictionary of Slang

a foolish endeavour, a pointless effort.

1890		‘’Arry on [...] the Glorious Twelfth’ in Punch 30 Aug. 97/2: These strikes is becoming rare noosances [...] Mug’s game. They’ll soon find out as the Marsters ain’t going to be worried.
1903		A. Binstead Pitcher in Paradise 147: Till two hours ago he would ha’ staked his little wad on Lou, which on’y shows you what a mug’s game plungin’ is.
1906		Sun. Times (Perth) 16 Sept. 4/7: The ole man [...] come at the mug’s game er shoutin’ beer n’ mussels for tarts wot was on at the Gaiety.
1910		Bulletin (Sydney) 28 July 32/2: jones: [...]. ‘No, I’ll not bet any more to-day. It’s a mug’s game.’ friend: ‘Ten to one you will.’ jones: ‘Done.’.
1914		Joyce ‘Two Gallants’ Dubliners (1956) 50: ‘I know that game,’ he said, ‘and it’s a mug’s game.’.
1923		Wodehouse Inimitable Jeeves 133: This ante-post betting is a mistake, an error and a mug’s game.
1933		T.S. Eliot ‘The Modern Mind’ in Use of Poetry and the Use of Criticism 147: As things are, and as fundamentally they must always be, poetry is not a career, but a mug’s game.
1936		J. Curtis Gilt Kid 131: ‘Mugs’ game drinking.’ ‘Yes? Well, there are a lot of mug’s games.’.
1944		J. Cary Horse’s Mouth (1948) 107: It’s a mug’s game, Coker, especially for a woman. You can’t get your own back.
1949		Wodehouse Mating Season 19: You [...] wonder if it wasn’t a mug’s game hitching up with her.
1956		J. Curtis Look Long Upon a Monkey 26: That was a mug’s lark.
1958		A. Sillitoe Sat. Night and Sun. Morning 21: It was no use saving your money year after year. A mug’s game.
1966		P. Willmott Adolescent Boys of East London (1969) 149: It’s very easy to get caught. I reckon it’s a mug’s game.
1971		F.J. Hardy Outcasts of Foolgarah (1975) 85: You didn’t ever marry, did you, Moss – well, not to worry because it’s a mug’s game.
1985		B. Humphries Traveller’s Tool 68: Unless you’re Jack Nicholson, don’t try climbing through a transom with a hard-on. It’s a mug’s game.
1993		I. Welsh Trainspotting 197: It’s [i.e. heroin use] a mug’s game, Mrs Renton.
2000		J.J. Connolly Layer Cake 28: He was one of the first to realise that taking libbos [...] taking the piss outta the old bill, was a mug’s game.
2011		J.J. Connolly Viva La Madness 383: Q. Trying to negotiate with madness? A. It’s a mug’s game, guv ... send ya mad.