I think those two sentences together are important. You are making yourself less of a person by thinking there is some "signal". There is no black and white NPD, for starters and trying to simplify/flip a switch and have magic happen is making everyone less of a person because people are not that simple!

With any person, any relationship, you have to consider yourself first. You have to work on your own balance, that's the only way you won't tip over. Concentrating on what the other person is/does is like trying to make the waves calmer so you won't be as likely to tip over.

Why don't you like people you feel are NPD's? Because they're "selfish"? If you cared about yourself and were "selfish" with yourself, you wouldn't be attractive to them. Don't do something to please someone else; only do things that please yourself! You come first always, because it's your life. One can't get or fit in someone else's life; there's no room; they're in there! Same happens with our life; that's why we get uncomfortable, that's what discomfort is for. Listen to the discomfort. Feeling resentful? There's probably a reason :-) Feeling good? Feeling angry? Feeling alone? Feeling sad? Feeling excited, curious, anxious? Listen to what you are feeling and follow it back to what is taking place/where it's coming from and then decide what you want to do with the knowledge.

There's nothing wrong with being friends, talking to, loving, etc. a person you feel are NPD. But don't throw the baby out with the bath water; all that glitters is gold, glass glitters so glass is gold is an easy to see error but deciding all "charming" men are NPD is the same error. You can't know what another person is like until you truly get to know them. If one first gets to know one's self, that makes the opportunity to meet others much more pleasant.