Johns Hopkins Psych finally said it: Malignant Narcissism

[politicat]

26. So... the developmental view of Cluster B is a fault around age 3.

Children at that age are deeply solipsistic -- they are the center of the universe. Which is fine, and good, because during language acquisition and early socialization, they need to be learning language and recognizing that they're unified beings. The problem is when someone gets stuck there. A trauma can do it, and sometimes that trauma isn't even significant enough to register for others. The birth of a sibling can do it because it takes away a caregiver's attention. But not always.

For the narcissist, they're not actually convinced the rest of us exist. And if we do, we don't exist the same way they do. They have a faulty theory of mind and cannot shift perspective. We're non-player characters in their single-player game -- we exist to give them rewards and to serve as targets. When we speak back, it's as offensive and unexpected as the little green army men objecting to being buried in the sandbox. But narcissism is also born in that failure of theory of mind, because a narcissist cannot generate their own self-approval. They have to seek it from others, and they're constantly being torn between wanting approval from the toys and not believing the toys have the right to comment.

So adding in sadism and aggression and antisocial behavior? It means they're even less convinced we're real, and have decided affirmatively that the toys aren't worth having, even for approval. That's why they're dangerous.

(And this is absolutely a 40K foot view, not the details.)