A person who, though seemingly well educated and intelligent, during the course of an argument proves themselves to be very ignorant and furthermore very persistant in espousing their ignorant beliefs.
A person who is persistently ignorant.
Mitt Romney: Corporations are people, my friends.
Person in the crowd: No they're not!
Mitt Romney: Oh course they are! Everything corporations earn ultimately goes to people.
Laughter from the crowd
Mitt: Where do you think it goes?
Person: Into your pocket!
Mitt: (really trying to make his point) Yes! into people's pockets!
Me at home: Didn't you go to Harvard?
Clean-cut college kid: Obama, he's the antichrist! (spouts off for ten minutes how all the signs in Revelations points to this)
A kid listening: How does he go here?
Another kid: The word for it is persignorant.