I appreciate the example and I think I see your point. I agree with the underlying logic, in general, but applying it to the N in NPD seems an over extension.
Dictionary definitions for the two terms, as records of common usage, are notably different. Autism refers solely to the condition so your example sentence would be an inappropriate use. Acceptable and understandable in the language, but an uncommon application of the word. On the other hand, narcissism is used for general egoism and self importance first and for NPD second.
This of course doesn’t invalidate your feelings when hearing the word or desire to protect others from the same, but maybe this can offer some comfort if the most common usage is not intended or even understood as a slur or even a reference to folks with NPD.



Oh hell yeah! NPCs trick my players all the time. Commanders, strangers, witnesses, priests, anybody might have an ulterior motive or secret agenda.
Best advice I have is just trust. Player characters don’t need to trust every non-player character but the human players at the table absolutely have to know they can trust you the human GM.
When my NPCs pull some shady stuff, like the reveal last session that leader of the crusade has been plotting to betray the PC crusaders for the entire campaign, that reveal always comes with a huge smile from me. “Yeah y’all, this dude is terrible! But now your characters are on to him and I can’t wait to see how they take him down!”
I’m not pulling one over on my players, I’m inviting them to a party I’ve been planning for ages and now we all get to find out what happens next.