Nor I in the 2010's/2020's; I have to assume GP is either significantly older than us, or from a community with a strong cultural bubble that may be clouding their judgement.

I experienced this at an boy's prep high school in the late 90s. It really was alienating to have friends I'd known since kindergarten start to refer to me by my last name out of sheer conformity.

I did in that timeframe. To be clear, it's not "Mr Surname" but just plain "Surname". I have a lot of friends like that, "Boughter", "Mooney", etc. Not everyone, but particularly if the first name was a common one or they played sports.

I'm actually surprised you're not familiar with the practice. Think Scully from X-Files or Stifler from American Pie.

>Stifler from American Pie

I always assumed it was his first name, thanks for expanding my understanding just a little!

Not just Scully, but essentially everybody from every doctor or police procedural goes by their last name. The shows aren't called Meredith's Anatomy, Gregory, Adrian, or Theo.

It’s mostly a thing among kids heavily into sports, in my experience.

I suspect the equivalent for 90s/00s nerdy types is e-mail addresses.

I am still "squirrel" to some college friends. And think of many of my college friends and co-workers as their username.