Green’s Dictionary of Slang

(orig. US) a fool, a simpleton.

[1896		Sacramento Bee (CA) 9 May 12/4: [advert] Our Kola Wine Braces up Tired, Weak and Lame Brains [...] in fact (it will almost clothe a skeleton)].
1914		Courier Post (Camden, NJ) 7 Mar. n.p.: [cartoon caption] Gosjh, I’d like to get a look at the poor ‘Lame-Brain’.
1919		C.E. Piesbergen Overseas with an Aero Squadron 70: John Cruigshank [...] It was really too severe to call John by the awful cognomen of ‘Lame-brain.’.
1922		Columbia Eve. Missourian (MO) 2 Nov. 7/4: The Tigers fight hard not only on Saturdays when the ‘lame-brains’ go to see the games, but also every afternoon.
1940		Times-Indep. (Moab, UT) 24 Oct. 5/4: Where are you going Lame Brain? his chum asked.
1944		N. Davis Rendezvous with Fear 24: Come in, lame-brain.
a.1946		‘The Open Book’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 115: Take the lame-brain from cold Colorado, / where high Pike’s Peak ponders and broods.
1951		P. Whelton Angels are Painted Fair 85: Okay, lame-brain, where are you?
1966		F. Elli Riot (1967) 44: The muscle-bound lamebrain was scared stiff.
1980		J. McClure Spike Island (1981) 189: Dirty-ankled, half-pissed lame brains with a collective I.Q. of forty-three.
1991		Desperate Dan Special No. 7 5: Of course! Samurai swords are all Japanese, lame brain.
2000		Indep. Rev. 12 May 10: A rebuke to the message-mongering of Hollywood lamebrains.