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Its a ruder version of 'gone belly up' meaning things have gone drastically wrong. A fish goes belly up when it dies, so maybe thats where it originated
Yeah curmudgeon, that's what I was going to say.
'gone belly up' is easily explained, and it naturally leads to 'tits up' . Just like how 'I can't be bothered' evolved to 'I can't be arsed'- via 'I can't be bovvered'.
Origin of expression 
Linear Mode
