Green’s Dictionary of Slang

an eccentric, a fool; also as adj.

1985		J. Wambaugh Secrets of Harry Bright (1986) 55: He’d been called Wingnut since Grammar school.
1990		S. Morgan Homeboy 22: Where is that tragic wingnut?
1997–2002		Hope College ‘Dict. of New Terms’ 🌐 wingnut adj. Describes a person who is unintelligent, stupid, or crazy.
2008		Simon & Price ‘Took’ Wire ser. 5 ep. 7 [TV script] Some wingnut starts killing people.
2018		Guardian 13 Jan. 🌐 [W]ingnut old hams who find themselves currently between jobs.
2018		Eve. Standard 11 Nov. 11/3: Mrs Obama [...] wrote ‘The whole thing was crazy [...] deliberately meant to stir up the wingnuts and kooks’.
2020		Twitter 10 Apr. 🌐 it also takes in far-right YouTube wingnuts, galaxy-brained celebrities, InfoWars, David Icke, Russia Today.