What Mulberry said, but just be aware that this guy likely won’t lose everyone. I’ve known someone like this before and cursed him in a variety of ways. The curses all worked, but he didn’t lose absolutely everyone. That may have been for my own personal development (so I could keep cursing him more), and if you think about it, people are unlikely to be completely socially isolated forever.
So what you can do is curse him to lose his good relationships and keep the shitty ones. They may not always appear shitty on the outside, but if he does behave how you describe and you make it even worse with magick (I have achieved this with demonic magick), this toxicity will be present in every relationship he has.
People like this tend to find “minions” or vampiric thralls that are extremely weak and easy to enact malice upon for the sake of narcissistic pleasure. These thralls also seek out people to treat them like shit, so these people tend to find each other pretty easily. I am not making a value judgement here, moralizing or making “good and bad” claims. That is just what happens in the world. I’ve seen it many times. I’ve even seen the same thrall get used by multiple narcissistic individuals, although one was far and away the stronger, more emotionally secure, and more intelligent of the two, and also just overall more fun to be around.
So the thing with all this is the fewer people there are in his life, the fewer targets he will have to offload his hatred onto, meaning he will have to put more on the few relationships he has left. With the guy I mentioned before, he mostly offloaded onto me cause I started distancing myself after I realized what he is and he didn’t like that, and he put all the rest onto his thrall. If he didn’t have me to hate, it would have inevitably gone onto one of the few other relationships in his life.
What this means is that you have a choice (probably). You can either keep this person in your life and engage in psychological warfare, or you can dip. If they remain, then you’ll get probably most of their hatred. Even if you do literally nothing aggressive other than curse him and watch as he tries to assault you over and over again, he will probably keep himself going with his own hatred. Really he hates himself, so he has plenty to project onto you. If you dip, then it is more likely that he will ruin some other otherwise kinda reasonable-ish relationships (reasonable enough for toxic narcissist standards). Maybe that’s his best friend, maybe that’s his partner. If you take this route you’ll probably never find out unless you are in overlapping social circles, so keep that in mind if what you want is vengeance.
The first curse I used was The Master Curse in Magickal Attack, by the way (well my first ever curse was one of the lesser curses from the same book, but on the thrall, who at this point the narcissist had turned against me). Also, by the way, once you learn their playbook narcissists (in general) are some of if not the most predictable people on the planet. I mean it’s kind of funny. They all do like exactly the same things, and those things are abundantly obvious if you know their patterns. I once had someone try to gaslight me twice over the same exact thing after she kept doing it over and over again, and then she tried to make me think I was at fault.
They essentially try to strong-arm their lies onto you and make you question your own memory and judgement so they can impose their false version of reality onto you. This can work on people who don’t realize what is going on, but if you know that this person is a narcissist and that they are clearly throwing hate at you, probably for no reason of your own, then it’s probably the least subtle, most obvious and brutish manipulation tactic out there. It works against the noobs, but go up against someone who’s aware of the realities of hatred and human malice and it’s like putting an aggro punk up against a trained martial artist. The artist is the one who will decide how that situation plays out.
Just be aware that not only will the toxic narcissists try to make you feel that you are the problem, so will the weak people they tend to attract and keep around them. Really these sorts of narcs are weak as well, they are just more aggressive. If I had to pick I’d absolutely be the aggressive one. I can understand the need to enact hatred onto others for the sake of emotional healing, but with emotional maturation this becomes less and less of an issue. Now I only really indulge in sadism if someone comes at me first, and then only if there is something for me to gain. Otherwise, I deal with them coldly and get them the fuck out of my life as efficiently and effectively as is possible because such pathetic people are not worth it. There is no satisfaction to be gained in beating up an insect that cannot even see you.