A person who is obviously weird, strange, and does retard-like things, but is a
fully functional human being,
or whatever species they are. Usually they are assholes, but they're usually
enjoyable and funny.
Example 1)
*
Gonzo screams "
Dick Waterfall" in the middle of an instructional period*
Jessica: What is wrong with that man
Amber: I don't know, but he must be a pretty functional kind of retard.
Example 2)
*Actual disabled child walks by*
Jessica: He's probably not a very
functional retardAmber: Dude, that's my brother.