...or you can reply with something totally unrelated.
Her: "out of your league"
You: "Man I love limes and salt, perfect combination" - keep dancing
----
Her: "out of your league"
You: "My 8th grade english teacher was gay" - keep on dancing
.....but still even better would be just to simply nod "yeah okay" and keep dancing. Ignore her crap, it has nothing on you... She just wants to make sure you can handle her.
So many guys... the first thing they want to do is react, "Its your loss!" and walk away... I mean c'mon put yourself in her shoes. If you blew someone off and then they were like, your Loss b!tch!!!... You would be like, whatever loser go cry in the corner like I know your going to.