Bad people who spend too long on social media call normies NPCs as in video-game NPCs who follow a closed behavioural loop. Wikipedia says this slur was popular with the Twitter far right in October 2018. Two years before that, Maciej Ceglowski warned:

I’ve even seen people in the so-called rationalist community refer to people who they don’t think are effective as ‘Non Player Characters’, or NPCs, a term borrowed from video games. This is a horrible way to look at the world.

Sometime in 2016, an anonymous coward on 4Chan wrote:

I have a theory that there are only a fixed quantity of souls on planet Earth that cycle continuously through reincarnation. However, since the human growth rate is so severe, the soulless extra walking flesh piles around us are NPC’s (sic), or ultimate normalfags, who autonomously follow group think and social trends in order to appear convincingly human.

Kotaku says that this post was rediscovered by the far right in 2018.

Scott Alexander’s novel Unsong has an angel tell a human character that there was a shortage of divine light for creating souls so “I THOUGHT I WOULD SOLVE THE MORAL CRISIS AND THE RESOURCE ALLOCATION PROBLEM SIMULTANEOUSLY BY REMOVING THE SOULS FROM PEOPLE IN NORTHEAST AFRICA SO THEY STOPPED HAVING CONSCIOUS EXPERIENCES.” He posted that chapter in August 2016 (unsongbook.com). Was he reading or posting on 4chan?

Did any posts on LessWrong use this insult before August 2016?

Edit: In HPMOR by Eliezer Yudkowsky (written in 2009 and 2010), rationalist Harry Potter calls people who don’t do what he tells them NPCs. I don’t think Yud’s Harry says they have no souls but he has contempt for them.