I've been dating this girl for about 2 weeks now. We've had sex a few times and things are going pretty good. The other night we had sex, and afterwards we went to go pick up her younger brother from work. He had to wait for 40 minutes for us. She told me before hand that he is a raging asshole to her. As soon as we got there, he got in my car and started screaming at her. He said some very cruel and demeaning things to her. He was yelling. I told him not to do that in my car, and he stopped for a little bit but started back up shortly. He basically told her that she's an idiot, she can't do anything right, and that he was supposed to sell some pot but couldn't so now she owes him money. This kid was out of control, way out of line. It was very difficult for me to sit there while he was talking to her like that, and based on what she told me about him, he does it to her all the time. She said he also blackmails her and various cruel things. He's only 17 years old too. My question is: should I kick his ass the next time I see him doing that to her? What if I checked with her beforehand? Or, should I just leave this one alone?