a douche bag
Somebody who thinks they’re super smart but acts like they know everything and it’s all wrong.
My math teacher is a douche bag. He says I failed but still thinks he’s the smartest person in the universe.
My cousin’s dog is a douche bag. It thinks it’s a genius but it can’t even sit still.
My brother is a douche bag. He says he’s going to be a rock star but he can’t even sing.