Definition of have a screw loose in US English:

have a screw loose

phrase

informal
  • Be slightly eccentric or mentally disturbed.

    • ‘Who could not think he has a screw loose after going on about seeing the devil on the stage?’
    • ‘People often say that it's harder to get out of the team that into it, but whoever believes that has a screw loose.’
    • ‘The first sign Backman had a screw loose was when he said at his introductory news conference that he intended to win immediately.’
    • ‘Some of my people have speculated about such things for a long time, but now it is official: it has been medically, clinically diagnosed that I have a screw loose.’
    • ‘Man, you have a screw loose in that head of yours!’
    • ‘There was a moment when I allowed myself to entertain the notion that maybe I was right after all, and the rest of the world had a screw loose.’
    • ‘My school friends had thought I had a screw loose when I stopped to stare, head cocked to the side, curiosity raging when the moving truck had first arrived.’
    • ‘So, filled with a hubris limited to those with more than a couple screws loose, he offs him.’
    • ‘She looked at her sister like she had a screw loose.’
    • ‘Most people didn't think he had an actor's profile; they thought he had a screw loose.’
    unstable, unbalanced, of unsound mind, mentally ill, deranged, demented, crazed, troubled, disturbed, unhinged, insane, mad, mad as a hatter, mad as a march hare, raving mad, out of one's mind, not in one's right mind, neurotic, psychotic
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