Green’s Dictionary of Slang

stupid, foolish.

1883		Altoona Trib. (PA) 19 July 1/6: The queen’s lameness has gone from her knee to her brain. A lame-brained queen is just as good as any other in these days.
1897		Las Vegas Dly Optic (NM) 18 Oct. 1/4: And yet there are lame-brained fellows [...] who talk of leaving such a heavenly climate.
1903		Montgomery Advertiser (AL) 9 Aug. 4/4: The record of the loose-jointed, lame-brained band of delectable junketers [...] should be effaced and forever.
1910		L.A. Times 9 May 6/3: A small installment of the [...] burning eloquence used in the French [electoral] campaign [...] bottom-of-the bath, emasculated, calf-with-two-heads, pettifogger, lame-brained, viscous [etc].
1928		J. O’Connor Broadway Racketeers 8243: The large rewards [...] naturally attracts the lame-brain species of gyp artist.
1940		J.G. Brandon Gang War 203: This is a hard-working police station, not a rest home for a lot of lamebrained loafers.
1943		Brattleboro (VT) 26 Nov. 10/1: Soldier [...] Calls W. River Dam Lame-Brained Dubs Scheme.
1951		M. Spillane Long Wait (1954) 133: Of all the lame-brain stupes you take the cake.
1964		L. Hansberry Sign in Sidney Brustein’s Window in Three Negro Plays (1969) I ii: I can’t stand it when you start prattling every lame-brained libertarian slogan that comes along.
1972		(con. 1916) G. Swarthout Tin Lizzie Troop (1978) 147: If wind of this lame-brain escapade gets out, we can put the horse, as an instrument of war, out to pasture forever.
1978		S. Longstreet Straw Boss (1979) 343: Except for a few [...] lamebrained halfwits.
1983		J. Byrell (con. 1959) Up the Cross 168: [T]he lamebrained act he pulled on the Wednesday arvo.
1986		L. Heinemann Paco’s Story (1987) 80: This Jasper — name of Rufus or Zebedee or Snowflake, or some lame-brained affair as that — must have been a busboy.
1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 20: This lamebrain girl named Kerwin runs into the same forest.
1999		Indep. Rev. 27 July 9: She’s in love with lame-brained Hero.
2004		Mad mag. Oct. 31: Fix delections and install leaders who are lamebrain shills for U.S. industry.
2005		H. Mantel Beyond Black 266: There are thousands of them out there, so pathetic and lame-brained.
2012		Valley Morn. Star (Harlingen, TX) 28 Dec. 4/4: ‘Guns don’t kill people, people kill peple.’ What a lame-brain excuse.