Mispelling of the word "retard". People suffering from insomnia dyslexia may accidently spell retard in this way, and when used as an insult, the word backfires in your face and only proves that you are the retard.
Man1- What's 2+2?
Man1- No, it's 4. You're a retetard.
Man2- I was being sarcastic and you're the retard because you can't spell.