The problem with diagnosing narcissism in real life is that the person with narcissism first has to admit that he has a problem. They don't just waltz into a psychiatrist's office and ask to be seen on account of everyone else saying they have a problem. Their first line of defense is denial. It is usually what they stick with so adamantly that everyone else who notices their issues, just backs off because it gets exhausting having to deal with these sorts.
Disclaimer: I am only responsible for what I say, not what you choose to understand.