"Long story short I dialed him sent him a death threat then blocked him."
What's up with the death threats nowadays, a simple fuck off would have been enough, a mentally unstable person might take it personally and end their life, it's not something that should be used lightly.
These days are tough on everybody. Most of my friends are functional mentally ill psychos, other more mellowed out chill nerds. But all I know, if shit goes down, it will be the first ones that will help.
It sounds like you fit your own description of mentally ill and lack of humanity. To be sending people death threat over his words. Being intolerant towards people itself is already pushing yourself on the path to be a fascists.
A lot of time we get upset by someone who exhibits the same characteristics as ourselves.
If you don't stay mindful about it you turn into the very thing you swore to destroy.
Leave it be and go your separate ways. By saying anything further just be pouring salt on the wound. I'm not saying he's in the right. But maybe in the future consider talking to the person about what's wrong instead of bottling it up. Because this is the result of bottling anger up. For your sake I hope the death threat isn't a voicemail or text message. That could go against you if your friend decides to get the authorities. Doesn't matter your age they don't take shit like that lightly.
sounds like you pulled a reverse. don't put your hate onto other people because you were having a bad day... let's hope the dude is dealing with it, death treats can be taken seriously to the point of criminal charges. also, there are some court cases appearing of people filing suit over these charges, causing depression, anxiety...
since that bullet (so to speak) has already been fired, the right thing to do would apologize and then return to block so you won't be tempted to do that again.
For some people it's better to be with an unpleasant person than to be all alone. You can reason with yourself and think, is it worth all the arguing? Or is it better to forget and move on? And I know how hard it is to make such a choice.