@Diverseopinions
I think a diagnosis is needed before it can be said with certainty that someone is a narcissist.
There are several problems with this.
Narcissists by definition have very little self-awareness. If they feel depressed, chronically angry, whatever, they will be holding other people as entirely responsible for that. And so they are highly unlikely to seek out a psychiatrist or someone similar and to say "I think the way I relate to people is problematic."
Many narcissists who HAVE been formally diagnosed have been seen by a psychiatrist after being charged with a crime. The involvement of mental health professionals has mandated by the judiciary. Or they have come to someone's attention due to an acrimonious custody dispute, that kind of thing.
Also bear in mind that narcissists by definition are very manipulative. They are especially manipulative of people in authority, which includes doctors! They often pull the wool over the eyes of even seasoned professionals.
Narcissists are especially good at convincing psychiatrists and others that it is their spouse and children who have a problem and not them. (I speak from experience.) Character-assassination.
I have read enough about narcissism to recognise it in two members of my own family. If a duck quacks, etc. I wouldn't dare to form that view of a casual acquaintance, there's not enough to go on and narcissists, also by definition, wear a mask when out and about. i really think you have to live alongside them to see them in all their dysfunction.