The worst thing about narcs are their inherent insecurities. So if you are someone who is naturally confident, these narcs will plague you your entire life.
Typically what you want to do in order to flush them out, is to drop things like, "I am not a professional or expert", or "I am unsure". You know, as if professionals are wasting thier free time corralling customers through anonymous venues, right?
They will pounce on any hint of insecurity as they have no means to discover the accuracy or validity of something indeendently from thier gut reactions. Now this isn't always what will define an NPD. However it's one of the first lures, then they keep coming and they never let up once you give a few nice shots to thier ego.
Typically it is called "trolling" in the mass narcissistic world of the internet these days, but way back when it was considered part of an "initiation" to a higher level of thinking and consciousness. Now it's just hell everywhere.
Personally I think they've been beaten or belittled to the point of have ZERO self esteem, in many cases, and they repeat the pattern of attacking others with perceived weakness where they envy the projected strength.
You know, the sterotypical pattern of learned behavior.