Green’s Dictionary of Slang

1. (US) a fool, a simpleton.

1876		St Louis Globe-Democrat 19 Jan. n.p.: They hear the saloon battle-cry of ‘Heraus mit him,’ followed by the bar-keeper’s observation of ‘that’s the kind of hairpin I be,’ and ‘how’s that for high?’.
[1877		Troy Herald (MO) 1 Aug. 3/1: Say, pa,...wasn’t Benedict Arnold a reg’lar snipe?...A crooked hairpin, you know; a shark, a sort of fraud generally?].
1879		in Bill Nyes Western Humor (1968) 12: That’s the kind of hair pin he is.
1883		Nat. Police Gaz. 20 Oct. 6/3: ‘Surely, sir, you have not experienced the loss of a cherished and devoted wife.’ ‘No,’ I made answer, tersely, ‘I am the other variety of hairpin’.
1907		W.M. Raine Bucky O’Connor (1910) 214: Threaten nothing! Collins ain’t that kind of a hairpin.
1931		‘Stampede’ in T. Goodstone Pulps (1970) 86/1: The third hairpin is none other than our own Dishpan Charlie!
a.1946		‘The Open Book’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 114: You can bet that I savvy the hairpins, / I know ’em for what they ain’t worth.
1968		K. Brasselle Cannibals 152: At seventy-odd years, this hairpin was still walking around.
a.1985		‘The Open Book’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 111: Take for instance the Panhandle hairpin, / widely known by the moniker ‘Tex’.

2. (US) a woman.

1927		C. Samolar ‘Argot of the Vagabond’ in AS II:9 387: A woman is a hairpin.
1931		Irwin Amer. Tramp and Und. Sl. 94: Hair Pin. – A woman, even in these days of bobbed hair.
1938		Eve. Post (Wellington) 25 Jan. 8/8: Modern Americanisms [...] The names for girls are legion [...] ‘Canary,’ ‘Hairpin,’ ‘Sardine,’ ‘Hotsie-Totsie’ or plain ’darb’.
c.1943		‘Bill O. Lading’ You Chirped a Chinful!! n.p.: Hairpin: Woman.
1953		E. Wilson Look Who’s Abroad Now 46: ‘I think I’ll be after goin’ down to the Royal Hibernian Hotel bar for a drop.’ ‘Sure, and your old hairpin will be after goin’ with ye’.
1961		B. Crump Hang On a Minute, Mate (1963) 23: They stopped in a small town for Sam to send a telegram to his ‘Old Hairpin’.
1966		P. Boyle At Night All Cats Are Grey 166: No use wasting your sympathies on that old hairpin.

3. attrib. use of sense 2.

1953

W. Brown Monkey On My Back (1954) 203: ‘There’s a party going on – a hairpin joint’ ‘A what?’ ‘Hairpin joint – bow tie party – lesbians.’.

4. (US, also hair-bones) a thin person.

1959

I. & P. Opie Lore and Lang. of Schoolchildren (1977) 189: Thin people inspire almost as many names [...] hair-bones, hairpin.

5. (Aus.) a despised person.

1954

(con. 1940s) T.A.G. Hungerford Sowers of the Wind 8: Norm’s been giving us the low-down on this hairpin, Lefevre.