We used the word “retard” to mean slow for a long long time. But when it became a psychological diagnosis, the colloquial usage shot way up. Maybe some of the people calling others “r*tards” were speaking French, but I think the majority were inspired by hatred. So, the people who care about these things did two things: we changed the name of the diagnosis, and we stopped using the word. People don’t use that word nearly as much anymore.

I think a similar thing is going on with that word you used. “N*rcissist”. It had a somewhat valid use in the 1800s for a while, but it pretty quickly became about a psychiatric disorder. In the modern day, the majority using the word are inspired by hate. I don’t think most people using it are hateful, but I think they got the idea from hateful people. NPD is really stigmatised, and I think the people who care about these things should do two things: we should change the name of the diagnosis, and we should stop using the word.