This retorical question is asked without expecting to recieve an answer.
However, if the person it is said to has enough guts to say: "Yes, I do!", you can say: "I am smarter than you, stronger than you, and more handsome than you, so shut the fuck up!".
Tip: Never use the expression when you do not really mean it. Remember that it can harm and insult a person more than many other remarks.
Montague: So you say you are better than me?
Capulet: In fact, I do.
Montague: You lie!
-Hahaha, you will never achive anything, you loser!
-You think you're better than me?!!