Labunchkin
A person who thinks they're the center of the universe and everyone else is just there to listen to their nonsense and admire them.
My dad is a labunchkin. He said he's the best at everything. He can't even tie his shoes.
My friend's cousin is a labunchkin. He said he's a genius. He can't even spell genius.
My neighbor's dog is a labunchkin. It thinks it's the king of the block. It barks at the mailman.