A piece of work
A total idiot who doesn't realize how clueless they are. They have all the brainpower in the world but still manage to mess everything up. People use this phrase when they want to sound fancy but mean something really rude.
My brother is a piece of work. He thinks he's Einstein, but he can't even remember his own phone number.
My boss is a piece of work. He acts like he's the smartest person in the world, but he doesn't know how to use the printer.
My neighbor is a piece of work. He thinks he's a genius, but he can't even fix a leak in his sink.