Red Action came over to take you surfing with her. Before you'd had the chance to say anything, your friend insulted her. Naturally, she got upset at being insulted, so she insulted your friend back. After a while, they start having a heated argument. Before you know it, they're about to get into a fight. "No one disrespects me in front of my girl!" She declared, getting ready to throw punches at your friend.  

You definitely wasn't expecting your girlfriend and your best friend to get into a fight. Now you have to decide if you're going to stop them or let them hash it out.