airhead
A 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!
airheaded
Frivolous, dim-witted, useless, and/or unintelligent. I can't believe I made such an airheaded comment. Ugh, I really wanted to impress them.