I did some reading up on this area of it once (so bear with muh instant pocket PhD-ism-ings), and as contradictory as it sounds, narcissists do have a noticible degree of self-doubt and self-loathing. While they act like the center of the universe and their everything is just so amazingly awesome, their constant need to prove the sheer massiveness of their perfection is, well, a BIG need. Think of any you know personally or famous ones and what not. Their self-possession craves being put on the stage for
validation. Not in a hug & pat on the head way, but they need the numbers, the applause, the adulation.
Wanna knock em down? Attack what they're most proud of not head on, but from within, their attitude towards it. Question their feeling, not what they think is the substance, and it's bucket of pissy jelly time.
Ok, the latter part of that was just me winging it, so that's just my doodling with how I see it.