I think walking out and not engaging was the right thing to do.
He's got a disorder. That isn't going to change. So whatever you have done on your part to manage your own reactions and not engage in drama will help you but it won't change that he has a disorder and he's going to do this from time to time.
In therapy, when he instigates a fight- this was called an "invitation to the crazy party". You got invited but you don't have to attend.
Underneath it all, I think the invitation to an emotionally charged interaction is a need for attention. One is paying attention during an argument. By not engaging you didn't reinforce this.
But he's still there and wants attention. He's human, like everyone else and humans want attention. I think if you are living with him, there has to be some interaction. When we take away attention to an unwanted behavior- that leaves nothing. The next part is to substitute a positive one and attention to that.
If he wants to gripe about the election, maybe time it. Say OK, let's talk about this for 10 minutes but then I need to leave for an appointment, or cook dinner or get groceries. Or a distraction. "Look, I bought cookies".
I know you think he's crazy and don't like him but you've chosen to live with him, and even if he were just a room mate, even room mates spend some time talking to each other. It makes things easier for you. That's the goal. If something is better for him and you, it's better for you.
If he threatens to hit you let him know that isn't acceptable to hit people and that if he continues, you will need to call for help. At his age and mental status, that is a 911 emergency evaluation for being a danger to himself or others.


