I spend a lot of time mulling this over, since my therapist thinks that both my SO and MIL have malignant narcissism.

What I can say about both of them is that they really find doing emotionally disruptive things absolutely vital to their lives. MIL likes to pit her kids against each other so she can watch them fight, and she smiles like a vampire who just had a delicious blood feast when she sees it. Her only grandchild develops an eating disorder? Nothing will do but to run out and buy her some size XXL pyjamas to make her feel worse. Everything for her is a provocation and meant to trigger a negative reaction, because that's what she gets off on. It's beyond being an asshole, it's pathological and emotionally disturbing.

My SO, one of the biggest examples is the gifts he buys me. They're usually highly thoughtful and unique, but they're also really for him (it's several times been a piece of art), and part of it is so he can take pictures of them for Instagram and display his fine taste in things to everyone. If I tried to move out and take those things with me, he'd probably break my arm. Nothing is really a gift with him, it's just a way for him to get himself something he can show off with. Or he'll spend a long time taking pictures of things we've bought on trips just to show what interesting and unique tastes he has and how therefore he's better than anyone else. It's really tone deaf and it really reflects how he doesn't actually enjoy anything, but rather what doing something or buying something will help to elevate his status in his mind. It's tiresome and tone deaf. It isn't that I don't like the gifts, but the whole point is that they're not really gifts at all, and my birthday or whatever is just an excuse to acquire something that makes him feel important. He really has no friends, and I think this is a desperate way to make the few people who try to be nice to him at least superficially on social media think he's important, but really nobody can stand him beyond the superficial.

I think an asshole would just not be bothered with anything so deliberately manipulative, but just be really careless with your feelings and react badly when they get angry. I think that's the difference is the deep rooted pathological nature of it.