Boundaries today

It's hard for me to set boundaries when my boundaries are already being overstepped. A roommate came to my door and accused me of stealing his two dollar soda. He was really unpleasant and looked down on me in a really condescending and degrading way. This is after I tried to help him with his technical problems with his computer. I think next time he knocks I'm not going to answer or I'll close the door in his face. I'm trying to enjoy my evening and to be nice on top of it when I'm interrupted by this new person who isn't even nice about crossing my personal space boundaries by insisting I interact with him when my door is closed for privacy, and interrupting my evening with something that does not have anything to do with a time pressured issue around comanaging the space or anything cooperative, just an accusation of theft. I am in the house around meal times every day, and he could easily ask me when I'm actually outside of my room if I stole his drink. Instead he seems to feel that he can just ask me for computer and technical advice and for the internet password and treat me as if I am the house manager and his personal IT assistant not even give basic niceties back in the form of courteous body language or a smile when asking me about his missing stolen shit.