PLEASE ADVISE A FRIEND
I have a friend presently going through this but she has been tolerating this guy because according to her she loves him so much and they even have plans of settling down. How many ladies can keep up with a man that always insults you at every given opportunity, Insults like you are very stupid, you are useless, are you mad, do you think I am your mate, and then hangs up on you often. That's exactly what he does to her often times, and even after he hangs up, she sometimes calls him back because he doesn't call back. Please your advice will do her a lot of good.
Well, if she is being bothered by his behavior then it's up to her to take action. Make her set some new rules in their relationship (peacefully and with mutual understanding though). If he trully feels serious about her then he'll accept the terms; if not, it may be a heartbreak but everybody needs to learn how to get rid of people bringing negative vibes to their lives.
Hope I helped
You need to show them what better is possible for them. Show how a respectful relationship looks like and how people in a respectful relationship treat each other. They must meet more people. The folks taking abuse seemingly wilfully are actually very vulnerable having psychological issues, so helping them should be done with care without accusing them as they don't do these things consciously. A tough job, but if you can help someone worth it.