Best Friend's Boyfriend

Ca
Hi everyone! So my best friend and her boyfriend have been together for about 6 months now. Right from the bat, my friends and I had gotten a strange vibe from him. Originally, he had asked her out on a date and she had said no. He then continued to tell everyone he knew that they were dating. So my best friend decided to give him a shot and go on a date with him. It went well, so they decided to make it official. Although, over the past couple of months, she's come to me crying her eyes out because of something her boyfriend had said or done. The most common issue is him getting angry at her for the most idiotic reasons, such as her "holding his hand the wrong way" or her "staring at him the wrong way". She came to me crying again about two weeks ago because her boyfriend had said that when he looks at her all he feels is hatred. At this point I hate this guy with all my heart. I've openly told my best friend how I feel about him yet she keeps crawling back to him. Now I'm not usually one to butt into other people's relationships but this is my best friend and I really care about her. What should I do?