Green’s Dictionary of Slang

upper crust n.

1. the head, esp. in boxing use.

[UK]Egan Bk of Sports 200: Sam’s nob had also been in pepper alley; and his upper crust was rather changed.

2. a hat.

1827
182718281829
1830
[UK] ‘The Will’ in Egan Anecdotes of the Turf, the Chase etc. 75: I give to Bob Logic, when I’m in the dust, / My new lilly topper and best upper crust.
[UK]Egan Finish to the Adventures of Tom and Jerry (1889) 309: I give and bequeath unto my friend, Jerry Hawthorn, Esq., my tile, my castor, my topper, my upper-crust, my pimple coverer, otherwise my hat.

3. the social élite, the aristocracy.

1823
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1990
[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 187: One who lords it over others, is Mister Upper-crust.
[US]D. Corcoran Pickings from N.O. Picayune (1847) 165: William Weithman, a loafer of the upper crust.
[US]Woodville Republican (MS) 1 Feb. 1/2: He is de ‘Upper Crust’ – / Ob all de well-born darkies.
[Ind]Hills & Plains 2 82: Little forms of writing [...] which the experienced strata of the upper crust find it most satisfactory to correspond with the lower.
[US]Charleston Dly News (SC) 28 Dec. 2/1: Among the ‘upper crust’ of darkeydom.
[UK]Man about Town 30 Oct. 57/3: [P]ortents shadowing forth future upheavals and disruptions in the ‘upper crust’.
[US]Schele De Vere Americanisms 646: Upper Crust, Upper Ten Thousand, and Uppertendom, with a host of similar crudities, owe their origin to the unfortunate taste of a writer of great ability and well-earned popularity, N. P. Willis.
[Aus]Bulletin (Sydney) 10 July 13/2: Some ladies belonging to the ‘upper crust’ in Sydney are to be seen incog., early in the fore noon [etc].
[UK]G.A. Sala in Living London (1883) Mar. 80: He is known only as a comedian of rare and precious qualities [...] moving us now to mirth in The Upper Crust, and now to tears in Uncle Dick’s Darling.
[Aus]Bulletin (Sydney) 9 Aug. 14/3: And now the upper-crust has any amount of small scandal to amuse afternoon tea’ers with.
[US]F. Dumont Dumont’s Joke Book 99: Only poor people eat punkin pi – and that’s right for punkin pi was never made for the upper crust.
[UK]Manchester Courier 16 Mar. 12/2: ‘He claims to be very swell, but he’s rather ordinary, isn’t he?’ ‘Yes [...] just between the upper crust and the under-bred’.
[Aus]W.A. Sun. Times (Perth) 2 Feb. 1/1: The play's ‘enthusiastic reception’ by Bungaree’s ‘upper crust’ was more Duff than puff.
[US] ‘Central Connecticut Word-List’ in DN III:i 23: upper crust, n. phr. The aristocracy.
[Aus]Truth (Sydney) 8 Dec. 6/6: They are runnin’ of their steamboat / Are that same ole huppercrust. / At a pace which, safe as houses, / Some day will their boilers bust.
[US]S.J. Perelman in Marschall That Old Gang o’ Mine (1984) 33: Coney Island [...] will always rank as the playground of the ‘upper crust.’.
[US]Charleston (WV) Daily Mail 29 Aug. 1/4: [advert] The Lowdown on the Uppercrust! Secrets of society playgirls.
[US] in G. Legman Limerick (1953) 191: There once was a handsome Haitian, / The luckiest dog in creation, / He worked for the rubber trust / Teaching the upper crust / The science of safe copulation.
[UK]‘Charles Raven’ Und. Nights 102: How little Barney knew about the habits of the upper crust.
[US]Milner & Milner Black Players 247: Independent call girl with established book of regular tricks. Can move in any circles, including ‘upper crust.’.
[UK]R. Dahl Revolting Rhymes n.p.: Ah, Piglet, you must never trust / Young ladies from the upper crust.
[US]R. Campbell Sweet La-La Land (1999) 180: Now the upper crust of La-La Land isn’t the same kind of crust as the crust in New York, Chicago or San Francisco.

4. any form of élite, e.g. criminal, but with no aristocratic implications.

1895
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1954
[Aus]Truth (Sydney) 5 May 1/1: Dr Lea, the latrest victim of the tyranny prevalent among the ‘upper crust’ in Her Majesty’s Knavee.
[US]E. Hunter ‘Vicious Circle’ in Jungle Kids (1967) 26: After this one I’d be in the upper crust, one of the wheels.
[Aus](con. 1940s) T.A.G. Hungerford Sowers of the Wind 154: Now the upper crust has gone [...] we can have some fun.

In derivatives

upper-crustdom (n.)

the aristocracy, the upper class.

[UK]G.A. Sala My Diary in America I 344: By his garb, the insubordinate child may have been a member of one of the first families in Uppercrustdom.
upper-crusted (adj.)

aristocratic, upper-class.

[Aus]Bulletin (Sydney) 18 Aug. 22/3: No one ever mentions a Limousine here; but it is an ordinary phrase among the American upper-crusted. It is merely a species of motor. Millionaire American never owns a motor – always a string of them.
uppercruster (n.)

(Aus.) a member of social elite.

[Aus]J. Byrell Lairs, Urgers & Coat-Tuggers 42: In fact this meant that he gave over most of his time to his hard-up buckshee patients and less to the uppercrusters.