A person of moderate or high intelligence who acts like someone who is retarded. Can be made into the adjective: fartarded.
Guy 1: Hey i just got a 100 on my math test!
Guy 2: sweet man! that was some hard calculus we had to do.
Guy 1: Yeah. I wonder what 2x3 is?
Guy 2: ...you're a fucking fartard
V. Similar to "shart"-ing, having fartarrhea is when a person thinks he or she is passing gas, but a gentle brown mist is expelled from the anus, creating a Jackson Pollock in the underwear. (See Jackson Pollock)
Susan and her friends were drinking soda when she was stricken with fartarrhea. Her shit stank!