Green’s Dictionary of Slang

linthead n.

also lintbrain
[SE linthead, a worker in a cotton mill]
(US)

1. an insignificant or lower-class person.

E. Caldwell God’s Little Acre 144: ‘You damn lint-head,’ Buck said contemptuously .
[US]J.M. Inks diary Eight Bailed Out (1954) 28 July 37: Cooey taymah, sir, you linthead.
[US]W.R. Burnett Little Men, Big World 43: He’d dealt with some bad boys in his day, but this lint-head was the only one who had ever actually given him goose-pimples. Why didn’t he go back to Arkansas?
[US]A. Green in Journal of Amer. Folklore [Internet] At one time or another Southern local colorists used these analogs for poor white: lubber, peckerwood, cracker, conch, sandhiller, redneck, cajun, woolhat, squatter, clayeater, sharecropper, linthead, swamprat, tarheel, hillbilly.
R.A. Peterson Creating Country Music 6: The music’s maker was the country bumpkin, rube, linthead, cracker, or hillican.
H. Mills Legionnaire 356: It must have been a terrible affront to all Mason stood for and held dear in life to have to associate with a white trash linthead.

2. a stupid person.

[US]C. McCullers Heart is a Lonely Hunter (2004) 17: Sometimes he talked like a linthead and sometimes like a professor.
[US]J.D. MacDonald All These Condemned (2001) 141: The house full of lintheads who would talk too much.