Intellec-tard

One who in spite of his/her radical intelligence is prone to being; socially inept, devoid of common sense or likely to perform bonehead actions.
The state of intellec-tardation may also be acquired through excessive use drugs or alcohol. This state may fade, however the actions and reputation may live on in infamy.

Billy was a bright kid, but had a bad habit of becoming an Intellec-tard after his 3rd beer resulting in drooling and an inability to shut up!