What's a cutting thing to say to someone who insults you?

My friend keeps jokingly insulting me. It's really annoying. I can't over react because when she says things like "ewww what are you doing here?" "oh my god go away".. etc...she is joking. well thats her cover up i think, she thinks it makes her look cool. Whats a smart and sy way to say something cutting back to her. I don't know any of her secrets.