I have decided that I would like to have locks on my doors.
What made you think you want locks on your doors.
I just don't want people inside my room.
It's okay to want privacy when you share a house with someone especially a roommate. If you pay for rent there then you should be able to do what you want to your own door.
I hate him so much. I don't like how he leaves a mess around and he's always breaking shit. I want to punch his face in so bad.
Your irritation is valid and I think the locks are an excellent idea, as you'll be able to distance yourself from him and maintain privacy. That said, you shouldn't punch him regardless of how you feel. This could end up in you being hurt and it will make your roommate situation even more volatile.