(slang) To be insane, irrational, or eccentric.
"You know he really has got a screw loose in his head somewheres, an' there ain't any one but what says he's the town fool, all right."
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Regional slang from around the English-speaking world — British, Australian, Irish, Caribbean, Nigerian, Filipino, AAVE, and the hyphenated-English dialects that make the internet sound local.
See all Regional & Other slang on Slangora.