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

When you eat dirt for the first time and leave your family to build a shack in the woods