Green’s Dictionary of Slang

cheeky adj.

[cheek n.2 (2)]

1. impudent, esp. in the context of a younger person failing to respect their elder.

[UK]Lloyd’s Wkly Newspaper 16 June 1/1: We shall not be deemed profabne in permitting the parsons to associate themselves in our mind with the ‘cheeky’ urchins of St Giles’s.
[UK]H. Kingsley Recollections of G. Hamlyn 259: ‘You will find, sir,’ said Lee, ‘that these men, in this here hut, are a rougher lot than you think for. Very like they’ll be cheeky.’.
[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor III 134/1: And, perhaps, that makes us cheeky. [Ibid.] 137/1: The girls are wonderfully cheeky at fairs.
[Aus]Bulletin (Sydney) 16 Oct. 9/4: Spurgeon is a ‘cheeky’ youngster.
[UK]Pall Mall Gazette 8 Nov. 2/3: The cheeky boy, with the natural ingratitude of youth, often makes a long nose at his master [...] [F&H].
[UK]Boy’s Own Paper 10 Nov. 82: It seems a pretty cheeky thing for a youngster like me to try his luck.
[Aus]Bulletin (Sydney) 19 Sept. 48/2: He’s too cheeky for my taste, any’ow!
[Aus]K. Tennant Foveaux 71: I’ve met some cheeky brats in me day.
[Aus]D. Stivens Courtship of Uncle Henry 97: A cheeky look came over his face and he chuckled to himself.
[UK]G. Kersh Fowlers End (2001) 105: It’s my money you’ll get, you cheeky little runt!
[Aus]F.J. Hardy Yarns of Billy Borker 93: He’s a cheeky mug. A joke’s a joke, but this is going too far.
[UK]B. Chatwin Songlines 52: The leading lawman of Tribe C had the unforgettable name of Cheekybugger Tabagee.
[Ire](con. 1970s) G. Byrne Pictures in my Head 66: The laughing, linking girls. ‘Get the last of the cheeky Charlies.’.
[UK]J. Baker Shooting in the Dark (2002) 124: Now they say it’s us, our personal hygiene. Cheeky buggers.

2. (Aus.) bad.

[UK]E. Hill Territory 443: Cheeky: Dangerous, poisonous. (‘Cheeky blacks’, ‘cheeky snake’, ‘cheeky yam’.).

In compounds

cheeky possum (n.) [possum n. (2)]

(Aus.) an impudent (young) person.

Shepparton Advertiser (Vic.) 18 Feb. 6/1: You do not want to believe all Poppet says about poor old Aunt Agatha. The trouble is that she was just a bit strict with him, he is such a cheeky little possum.
[Aus]Sporting Globe (Melbourne) 9 Aug. 12/5: The ‘cheeky possums’ from 3DB will include Globe cast-off George Andrew and his "twin," "Puddin'" Casey, Morrie Callard, Norm Spencer, Danny Webb, John May and Athol Coates.
Tahrunka (Kensington, NSW) 9 May 3/4: This Uncle Rhemus of Alexander Mackie [College] referred to the S.R.C. as a lot of ‘cheeky possums’ being naughty enough to question the Principal's rules. This patronising attitude [...] has further unified the S.R.C. in their intention to assert their dignity and strength.

In phrases

run cheeky (v.)

to act or speak impudently.

[UK]Sussex Agric. Exp. 13 May 5/3: Defendant said he pleaded guilty to hitting the lad because he ‘run cheeky’ [...] Witness ‘cheeked’ him [and] the defendant knocked him down again.