So yes... self-protection, distrust, and honestly... fear. Most people I interact with on a daily basis work within the same general social rules as I do, but people with NPD do not. I am afraid of them because I cannot count on them to act within the normal social guidelines, and they very well might end up hurting me.

Yikes feeling scared of anyone is a handing that person a free power trip ticket if they become aware of your feelings. Personally, I don't think it can be isolated to only NPD's. As long as you can count on yourself to act within the normal social guidelines without being afraid that an NPD is going to undermine you in some way, that's the part of yourself you need to explore.