Today in the news a recent college graduate is suing her school over a sexually active roommate. The student was doing well until her senior year when she began living with a new roommate. According to the complaint the roommate was also engaging in sexually inappropriate video chatting while she was in the room. The girl eventually left the school and finished her degree from home.
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.