flattie, n.¹ — Green’s Dictionary of Slang

flattie n.¹

also flatty

1. a dupe, a naïve countryman.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 218/2: For they betray to the ‘flatties’ (natives) all their profits and proceedings. [Ibid.] 406: It was only 4s. or 5s., but then I was only a flatty or I could have made 14s. or 15s. at least.
1873		Sl. Dict.
1880		Leicester Chron. 6 Nov. 9/1: She’s an out an’ out ‘flatty’.
1886		W. Newton Secrets of Tramp Life Revealed 9: Flatty ... One who does not understand the Cant.
1903		Tacoma Times (WA) 28 Dec. 3/6: ‘But I can’t get the fist,’ objected Jim. ‘Practice it, you flatty!’.
1909		J. Ware Passing Eng. of the Victorian Era.
2019		P. Baker Fabulosa 292/1: flatties [...] 2. dupes.

2. (Polari) a man, esp. as a member of an audience.

2019		P. Baker Fabulosa 292/1: flatties noun: 1. men (especially those who make up an audience).
2023		R. Milward Man-Eating Typewriter 121: [F]elching the trummuses of those destestable arroganki gillies and flatties.

flatty-cop (n.) [cop n.¹ (1)]

(Und.) a policeman who lacks sophistication in dealing with the underworld; a country policeman.

1865		Leaves from Diary of Celebrated Burglar 18/1: The ‘flatty cops’ took in hand to hunt up Jem and Kay, whom they heard, from those around, were the parties implicated.
1867		Memphis Dly Appeal (TN) 12 Mar. 3/3: The police are generally known as ‘flatty cops’.
1891		Emporia Dly Repub. (KS) 28 Apr. 3/2: A ununiformed officer is a ‘flaty [sic] cop’.
1916		A. Stringer Door of Dread 53: ‘Well,’ sez the flatty, showin’ his badge [...] ‘I’m goin’ to gather yuh in, and I’m goin’ to do it right now!’.
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 4: Flatty or flatty cop: Uniform policeman.

flatty-ken (n.) [ken n.¹ (1)]

a public house that is frequented by members of the underworld but where the landlord remains oblivious of their activities.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 243/2: ‘Flatty-kens,’ that is, houses the landlord of which is not ‘awake’ or ‘fly’ to the ‘moves’ and dodges of the trade.
1861		Melbourne Punch ‘City Police Court’ 3 Oct. 234/1: The Mayor.– Well my flying sawney hunter [...] you were reported to me as being scammered with some multee kertever flue fakers in a flatty ken.
1870		Hotten Sl. Dict.
1895		Crowe Aus. Sl. Dict. 29: Flatty Ken, a publichouse whose landlord is ignorant of the habits of the thieves and tramps.