I’m not NT, and I was not necessarily bothered by what Rhett said, but it was clear to me that this problem is all in his head.
Not everyone enjoys group things in the same way! Like you said, I don’t mind being on the outside of group activities. It doesn’t mean I’m a buzzkill and most people don’t mind. The few that do definitely are like Rhett ‘taking everyones personal enjoyment upon themselves to deliver’ and feel offended by someone who isn’t overtly displaying enjoyment and participating.
Good god I hope he’s not pointing this out to the ‘buzzkills’ because it is so fucking unhelpful to have someone try to force you to have fun and just makes that pushy person the ACTUAL buzzkill, making everyone uncomfortable. I had a friend of friend who would do this to me frequently when I was younger. Say if there was a conversation in a large group where I didn’t feel the need to add anything but was still really enjoying the ~vibes~ , he would turn to me and repeatedly question why I was so quiet and why I didn’t have anything to say, which would make me even quieter and want to not be there at all.
Anyway, I also hope Rhett can pull his foot out of his mouth and see that, like Link said, this is his problem, not the person he thinks is a buzzkill.