A person with narcissistic personality disorder possesses at least 5 of the following 9 criteria, typically without possessing the personal qualities or accomplishments for which they demand respect and status:

1. Grandiosity with expectations of superior treatment from other people.
2. Continually demeaning, bullying and belittling others.
3. Exploiting others to achieve personal gain.
4. Lack of empathy for the negative impact they have on the feelings, wishes, and needs of other people.
5. Fixation on fantasies of power, success, intelligence, attractiveness, etc.
6. Self-perception of being unique, superior, and associated with high-status people and institutions.
7. Need for continual admiration from others.
8. Sense of entitlement to special treatment and to obedience from others.
9. Intense envy of others, and the belief that others are equally envious of them.

Narcissism is considered a disorder because it is debilitating. When the ego gets so strong that it creates an imbalance making them incapable of empathy, it makes it very hard for them to learn or grow. They tend to learn by doing whatever it takes to get what they want, and many eventually learn that it's easier to get what they want when they're not being a total asshat. So they eventually start to focus more of their time learning which behaviors make them an asshat. They don't understand the feelings associated with it, because they don't ever really doubt themselves, but they do understand cause and effect. They can at least learn to become functional out of necessity.

A Narcissist's Prayer
That didn't happen.
And if it did, it wasn't that bad.
And if it was, that's not a big deal.
And if it is, that's not my fault.
And if it was, I didn't mean it.
And if I did...
You deserved it.