a clown
A clown is someone who looks in the mirror and thinks they’re the star of the show, but everyone else just thinks they’re a joke.
My brother looked in the mirror and thought he was a rockstar, but I just laughed at him.
I looked in the mirror and realized I was a clown because I forgot to brush my teeth.
My friend looked in the mirror and thought he was a superhero, but I just called him a clown.