My little brother spit on my mother, what should I do?

He's 18 years old and has really bad anger issues. He calls me, my mom, my dad and my sisters b*tches, as*holes, etc. He throws stuff all over the place and breaks things when he doesn't get what he wants. So today he got mad because my mother wouldn't give him any money so he spit at her face and called her a b*tch, this is not the first time that this has happened. He immediately ran away and my mom was SO PISSED! She said that that is it, but like before, she lets his punk but right back in the house. What can I do to stop this kid that wont result me landing in prison? My parents refuse to kick him out (because he's oh such a great kid), and my mom forgives him everytime. What can I do?