I'm curious around an issue I've seen some NPD individuals do, though not all. It might be more related those with some schizoid tendencies? I have observed some individuals with NPD to mimic other people's facial expressions. I'm aware of the difference between BPD and NPD. This is most definitely something I had seen with some NPD individuals. With one NPD person, he would mimic my own face expression almost exactly and seemed to be unaware. It was a little bizarre because my facial reactions are a little unique and cartoon like, so they looked pretty strange on him. Before I got to know him better, I thought he might be on the spectrum for a variety of reasons. But then it became clear it was NPD.
I've seen him specifically mirror my face expressions. But in addition, as I have gotten to know folks around him better, I have noticed he hodgepodged their styles and specific facial expressions like a cobbled together frankenstein monster of sorts. His happy pleased smile imitates a close colleague. His attempt at bonding face imitates exactly another eager colleague. His only real expressions are when he is disgusted / irritated/ elated at some punishment he managed to covertly dole out/ or blank.
My father was diagnosed in the late 60's as ASP ( sociopath at the time) and denied entrance to the military based on that which upset him greatly, though he had some pride in he diagnosis. He was a doctor, but almost did not make it through medical school because he accidentally killed too many people and did not have feelings about that. The medical school made him choose between dropping out and becoming a pathologist, so he became a pathologist. Even though he has many ASP traits, I think he is more NPD. He often gets financially duped by people who are likely more ASP than him because they flatter him.
He does this mimicking also, but only when he wants something from someone. It's not only faces he will copy. He will even copy impressive childhood stories that he heard from others and claim they are his own if he thinks it will get him somewhere. Otherwise, he could care less about anyone but himself and also acts a bit like someone on the spectrum when not performing for an end goal with an audience.