There's always a vulnerability or a handful of them that everyone possesses, that will always uniquely wound them when the vulnerability gets struck at all. I've never known what to call it though I would suppose these vulnerabilities do tend to fall into the narcissistic injury realm.

I have a huge ego, but it's decidedly not fragile. People have tried to bruise my ego and one person tried to outright shatter it. That woman failed, miserably.

Narcissists are actually very easy to topple once you know how they work.