Yeah, my parents are totally going to do that.

You could stand one up and your parents join it? Yes, not everyone can stand up their own self hosted stuff. In fact few of us can. There's a huge missing gap between your phone/desktop applications and just installing and running hosted applications, but I digress.

I stood up a Mastodon instance and invited a bunch of my friends. Only like 3 of us use it, but it's up and connected to the greater Fediverse.

No need to go that far. Maybe one HNer even does that or even wants to do it.

Or join an existing social network with a billion plus users.

Google+, now's your time to shine!