No it's not dyslexiclatin, 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?
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).
Precedes or follows either a gratuitously disrespectful or honest remark, originated in New York City. Used in similar fashion to "no offense" or "to be honest," interchangeably.
Ya mans is wild buns, respectfully. Respectfully he's washed.
After school, The Modells on Jamaica Ave was active. Respectfully.