A vivid vulgar simile meaning thoroughly, hopelessly crazy. The image evokes the frantic, chaotic behaviour of a rat trapped in an outhouse. Used to emphasise extreme, unpredictable, or erratic behaviour. More colourful and emphatic than simply saying someone is 'crazy' — the phrase signals a complete absence of rational behaviour.
Anyone who tried that stunt without a safety harness was crazy as a shithouse rat.
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(simile, slang, vulgar) Thoroughly crazy.
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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.