What I’ve learned:
There is, with very rare exceptions, no excuse for being an asshole. It is almost never justified. The easy thing is just always assume there’s no justification because if you think there is, you’re probably wrong.
Learned recently; my favorite pathology: the narcissist with ADHD: Can’t do anything terribly well but is completely convinced he does everything perfectly well, and cannot acknowledge the possibility that he can make any mistakes. (My present “position’s responsibilities includes being to blame for everything and anything. But then, this person is a gratuitous asshole.)