No it's not dyslexic latin, moreover it translates to "Oh I thought you meant you don't want it."
It is a surrogate phrase for the latter, often used in shocking scenarios, be that a debate, an argument or in a moment of intense revelation.
Legend has it that it was coined in Rushden, Northamptonshire - although this was never officially verified
Person 1: OI, WHERE'S MY FOOD?!
Person 2: OH I THIUGJY YOU EMANG UOU DOING WNAY UY!
Person1: eh?
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