a toxic person
Being a toxic person means you think you're the best, but you're actually the worst. You act like you're a hero, but you're just a loser who can't be nice.
He said, 'I’m the best, you’re the worst. I’m a hero.'
He posted, 'You’re a total failure. I’m the best. Also, I eat pizza for breakfast.'
He messaged, 'You’re not even cool. I’m the king of the universe.'