Green’s Dictionary of Slang

an eccentric, an odd person, a lunatic.

1955		B. Hill Boss of Britain’s Underworld 155: One or two nut cases tried it on now and then.
1956		‘Raymond Thorp’ Viper 115: Most of them are alcoholic or near nut cases.
1958		F. Norman in Encounter Nov. in Norman’s London (1969) 48: It may sound as though I am a nut-case.
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 44: I’ve copped a couple of flamin’ nutcases.
1968		P. Barnes Ruling Class I vii: Yes, he’s a nut-case all right.
1971		R.D. Pharr S.R.O. (1998) 229: ‘You’re really working out of a fruit and nuts bag today’.
1972		P. Fordham Inside the Und. 147: Anyone in the ‘nutcase’ line is reckoned to be good, clean fun.
1987		B. Chatwin Songlines 136: Bit of a nut-case, really.
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 57: I heard Pepper call out, S‘orry Mrs kennedy, ’ just like a little kid. God, she was a case.
1997		C. Hiaasen Lucky You 10: Sinclair wanted to make clear they weren’t nutcases.
1999		Guardian Guide 2–8 Oct. 87: She’s also got a ‘fruit and nut’ case [...] showing an unhealthy interest in her.
1999		R.G. Barrett Wind & Monkey (2013) [ebook] Les was still curious how Digger could turn from little Miss Goody Two Shoes, church on Sunday, into such a mad raving case overnight.
2002		J. Lerner You Got Nothing Coming 12: A new fish like you is gonna get eatenin the joint anyway — no need to advertise you been locked down with the nutcases.
2006		D. Mitchell Black Swan Green 115: Flamin’ nutcase, that girl.
2012		(con. 1980s) I. Welsh Skagboys 304: It’s hard to imagine that Tommy, being such a nice guy, was friendly with a nutcase like Begbie.
2012		D. O’Donnell Locked Ward (2013) 65: He was in fact a religious maniac. A complete cake of Religious Fruit and Nut.
2013		D. Whish-Wilson Zero at the Bone [ebook] The usual Fremantle crowd. Workers and Abos and deros and Rajneeshees – every third person a nutcase.
2019		A. Parks February’s Son 266: He may have been [...] a borderline nutcase but he was still a psychiatrist.