A frivolous, dim-witted, useless, and/or unintelligent person. I can't believe I got paired with such an airhead for this assignment. He's not going to get any work done at all!
airhead
and airbrain
n. a stupid person. (Someone with air where there should be brains.) Some airbrain put mustard in the ketchup dispenser. Bart seems like such an airhead, but he’s all heart.