Green’s Dictionary of Slang

(orig. US) stupid.

1939		W. Stegner On a Darkling Plain 107: You’re just a knuckleheaded farmer girl.
1948		Lay & Bartlett Twelve O’clock High! (1975) 139: That knuckle-headed Kraut navigator sure bitched us up.
1957		H. Simmons Corner Boy 63: Take that Rudolph fella. A knuckle-headed athlete.
1961		R. Gover One Hundred Dollar Misunderstanding 107: Jimmy bein so rump-thumpin knuckleheaded dum.
1977		R. Coover Public Burning (1979) 99: That goofy, knuckle-headed Incarnation of yours keeps repeating that.
1979		D. Maitland Breaking Out 169: You are a bloody lop-eared [...] knuckle-headed [...] fart-faced flip of a fucking galah!
1990		N. George ‘CPT Time’ in Buppies, B-Boys, Baps and Bohos (1994) 61: He’s got the youth and understanding to challenge Compton’s knucklehead rappers on their own turf.
2004		C. Hiaasen Skinny Dip 211: The same knucklehead politicians whose loyalties he had purchased.
2005		Health Insurance Underwriter July 🌐 [heading] Hall of Shame Spotlights Year’s Most Brazen, Tragic and Knuckleheaded Scams.