Oblivious douchebag
A person who's so blind to their own stupidity they think they're the smartest person in the room, but everyone else just wants to scream.
Thought he was the best at math, then got a D on a test.
Told me he was going to be a superhero, then ran into a wall and fell over.
Argued with the principal about why he should get an A, even though he failed the whole class.