tard
Any person who is not developmentally disabled, but rather has what is considered normal cognitive faculties but for whatever reason has opted out of using it.  Whereas mental retardation is genetic in nature, this form of behavior is environmental usually resulting in too much daytime television, Brittany Spears piped in pop music, and other environmental factors.
That dude right there with the five kids he took to see the movie Basic Instinct Two who has an InSynch ringtone blaring through the movie theatre drowning out the lame dialogue is a tard.  (2) That tard who thought he could drive a mile in front of me and cut in front of all of us in traffic is definitely a tard. (3)  The fact that dude just asked who wanted to chat in a chat room is a citizen of Tardania.