An abnormally obnoxious know-it-all, but brainless, individual who always has an answer, or factoid about everything, or "has done that too" but better than you. However, everyone knows better.
There goes that bobblehead Dan saying that, "the store's OPEN sign is in violation of the National Epileptic Associationstandards!"
A person with a head that seems out of proportion in comparison to his/her body. Rather than a large head and small body, a person who is a reverse bobblehead would have a large body and a small head.