How do I get a guy to stop flirting with my girlfriend?

this guy keeps slapping my girlfriends butt, and telling her he wants to screw her and things like that, and im not shure what to do.How do I get a guy to stop flirting with my girlfriend?
Tell him not to do it. And, if he keeps it up clean his clock. If you do not want to fight then get creative. Good luck.

PS - Update your question by posting the guy's name, address and phone no. He should get a few unpleasant calls.How do I get a guy to stop flirting with my girlfriend?
Tell the guy to stop. And if he doesn't, scare him by reporting him for sexual harrassment. You shouldn't have to do it, she should (if she cares about you). If she doesn't do anything ,she likes the flirting or she doesn't want to be known as a ';snitch.';