special unit
An intelligent person who is prone to making extremely stupid/idiotic mistakes.
Bob: What is a spoonerism?
Billy: It is when you have an sneurysm while apooning
Bob: Billy, you would be a special unit if you were intelligent.
Billy: But I am smart! My I.Q is -41
Bob: Why are you so stupid?
Billy: My mom is my sister!
Bob: That explains it.
Billy:My family tree has no branches!
Bob:Shut up.
Billy:I am a special unit!
Bob: If you don't shut up, I will kill you in the face.