Legal Question in Landlord & Tenant Law in California

You can make your vulgar roommate leave. If he has committed something that is obviously dangerous or illegal, such as using drugs or being violent, you can serve him with a 3-day notice to get out. Ordinarily, in your situation, your roommate is a month-to-month tenant, so you will need to serve him with a 30-day notice to quit. There are lots of 30-day notices on the internet.

Once you hand him the notice, the 30 days starts. If he doesn't leave, you can bring an "unlawful detainer" action against him, where you can get a judgment, ordering him to get out. If he doesn't follow the judgement, you can have the local law enforcement agency get him out.