Green’s Dictionary of Slang

shit-brained adj.

also shite-brained
[shit n. (1a)]

stupid, brainless.

[US]E. Thompson Caldo Largo (1980) 272: Here! Over here! Look over here, you shitbrained fuckers!
[US]B. Hamper Rivethead (1992) 69: Many is the time I felt I was going to go stark raving shit-brained wacko.
[Scot]I. Welsh Trainspotting 178: This one’s for you [...] Rambo, or Tyson or whatever the fuck your shite-brained fuck-wit of an owner has dubbed you.