have a screw loose
  1. (slang) To be insane, irrational, or eccentric.
    • 1871 July – 1873 February, Anthony Trollope, “The Major”, in The Eustace Diamonds. A Novel, New York, N.Y.: Harper & Brothers, publishers, […], published 1872, OCLC 1332510 ↗, page 306 ↗, column 1:
      Richard, glorious in new livery, [...] went with his sad message, first to the church and then to the banqueting-hall in Albemarle Street. "Not any wedding?" said the head-waiter at the hotel. "I knew they was folks as would have a screw loose somewheres. [...]"
    • 2010 July 16, Alessandra Stanley, "Television: Back to Work for ‘Mad Men’ ↗," New York Times (retrieved 16 June 2016):
      Pete Campbell (Vincent Kartheiser) would be just another irritating office brown-noser, a prep school Sammy Glick, except that he too has a screw loose and a mystical rapport with firearms.

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