How can I get rid of my mother's so called boyfriend?

He has 4 children that he has not taken responsibility for. Not only does he sale drugs, but he snorts crack on occasion. He has no job, no money in the bank, no house. He lives and mooches off of his sister. A complete bum! It is obvious that my mom is out of her sane mind. Me and my mother are well known in our community and if she gets pregnant by him our reputations are destroyed. I really need advice on how to get through to my mother to let her know that there are many other available men who are smart and successful. She has a good job, great life and this so called boyfriend wants to take major advantage of that. Me and him also dont get along AT ALL!!!