Wait, what Flintstones am I supposed to have watched? The Hana-Barbera cartoon was so good that it deserves to be the go-to example for things that young people "somehow haven't heard of"?
I think any of it. I haven't seen a full episode myself and I'm not that young at this point.
In general, it's now just stuck in my mind as a stand in for any sort of thing. I think there's an XKCD for this sort of thing (and XKCD may be close to being something you have to be over some age to know about). In general, just consider that someone not knowing something is a joyful time to introduce them to something new, instead of scolding or being disappointed they don't understand it.
Love your advice about being joyful about the opportunity to introduce people to new things!
I think maybe I need to learn to be joyful about also re-introducing things to people who probably knew the thing at somepoint, but have since forgotten. (Generally applies to people older than their mid 30s)
As an "old guy" with a literal gray beard, I think it's really important to remember to be joyful when explaining things.
Sometimes my computer experience is more than twice the life experience of someone I'm explaining something to ( in years at least :^D )
Honestly, the harder ones are when I'm explaining something to someone in the 40s (or older) who it seems "should have known" something, but for some reason either forgot it or never bumped in to it in the frist place. I often make the wrong assumption that they should've known it, when really, that's just a personal bias based on my own experiences.