Joke answer: Buy an air horn. Real answer: Try talking with your roommate about it first and be clear that their actions are making you extremely uncomfortable and you'd prefer them to not do those things when you're around. If they don't stop after that then it's time to have a chat with your RA or resident hall director about changing rooms. If that's not possible the extreme solution is to try to move off campus.
My college years were 1964-68, and this would never have come up. Respect for each other's space must be enforced. Has common sense been left out of current college campuses? Priority must be given to the main reason for being in college: studying. The offending roommate should have been reprimanded and then moved if necessary.