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?
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi
May I have an order of regular degular buttermilk pancakes? Without all the added jazz? Hold the blueberry smiley face, strawberry glaze, chocolate chips and whipped cream.