I don't know if many of you are going to like this answer, but it's nearly impossible to "talk" a friend out of a bad relationship. You've probably already tried. Have you noticed how no matter what you say, she don't listen to you? Have you noticed that even though all of your friends can't stand her boyfriend, and her parents want to kill him, she's still with him? She's probably heard people tell her "You deserve better" a thousand times. But she's not hearing it. She doesn't want to believe that her boyfriend is wrong for her, because for whatever reason, she loves the little fucker. I know, I know, you're like "How can you love someone who hurts you?" That's a very inquisitive question, you. I wish you would stop asking questions…anyway, the answer is that if you've never been in that situation, you won't be able to understand that it's hard to control who you love, even when they're wrong for you. Despite all rationale and logic, people stay in love with hurtful people all the time, and that's because love, although certainly deliberate at times, is a largely unconscious event dictated by hormones and other biochemicals that you cannot always consciously control. On a physiologlical level, love happens when a certain person elicits a chemical response in your brain because your body picks up on biological markers that tell it that person would be good for you. Whether that means that the combination of your genes would make a hell of a super-baby, or just that that person could protect you adequately, a large part of love is informed by what evolutionary benefit your lover brings to you. The rush of brain chemicals this brings about is very similar to addiction to a drug like cocaine or nicotine. When that person (or drug) goes away, the body literally goes into withdrawal. And I dare you to try to fuck with that by telling her "He's not good for you." That's not constructive. Your friend can't control herself; she is physically addicted to this dude. So, there is not one thing you can say, or one conversational tactic that will just magically change her mind about him. The best thing that you can do is be the most supportive friend you can be, because chances are, she knows that he's a slimy pip-squeak. All you can do is make it clear to you how you feel about him, not how she should feel about him. I'm sure she complains constantly about him; try to be understanding. The most constructive thing for her that you can do is just listen to her; be a sympathetic ear and take her side of the argument. Know that this is a couple that is clearly not meant to be, and that they'll break up at some point…and then you and I can key his car.