I have a guy friend who asked out a really mean girl. What should I do?

Actually this girl is more than just mean! She has a huge reputation of saying yes when a guy asks her out, and then not showing up at the date and laughing about how stupid the guy was to think she was serious. Unless, of course, the guy who asks her out is super popular. I actually over heard her talking about this guy after he asked her out and laughing about what a dork he is. My friend is not super popular, not extremely attractive, (not ugly, just not super good looking), and not her type at all. How can a save my sensitive friend from getting hurt without making him mad at me? He was just so happy when she said yes and I don’t think he will want to hear a word against her.