Retarded

An adjective originally coined by the professional medical community to denote an individual who was "delayed or held back" in perpetuity since birth, or shortly thereafter. Colloquially, it pejoratively assumes an individual was previously tarded at some point, and is now RE-tarded.

Tim: You just tried to skate down that hill with no wheels on your board, that's retarded man.
Tom: Piss off wankercheese, I've never even been tarded before in my life.
Tim: Well you are now asswaffle!!