have got a screw loose
To be or seem particularly silly, eccentric, crazy, or mentally unstable. (Also worded as "have got a loose screw.") That guy on the corner has definitely got a screw loose because he's been standing out there yelling obscenities at passersby all morning. My old uncle Pete has got a few screws loose, but he's a really nice guy. What's the matter with you? Have you got a screw loose, or what?
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