Do you know how to deal with a bad roommate? You never let them in to begin with. Once they’re in, it’s like bedbugs. You might have to go scorched earth to get them out.
The folks are hurt because home is your safe place. The rest of the world is chaotic, but you should be able to come home to peace. Instead, you find Derek in the living room clipping his toenails onto the carpet.
How to deal with bad roommates? Harsh, honest communication. You’re gonna have to say some uncomfortable stuff to a grown-ass adult. Or, you can just call them out online and let the commenters do what they do. I prefer that one.