have a loose wire
To be or seem particularly silly, eccentric, crazy, or mentally unstable. That guy on the corner must have a loose wire or something, because he's been standing out there yelling obscenities at passersby all morning. My old Uncle Pete is a nice guy, but he definitely has some loose wires. I mean, he's convinced the moon landing was a hoax. What the heck is the matter with you? Do you have a loose wire, or what?
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