Do you have some examples?

There are very very few things that could even hypothetically kill us all, so I'm curious if you grew up being passed around a series of apocalyptic doomsday cults or something?

Nukes. If you grew up in the 50s, 60s, 70s or 80s the specter of nuclear annihilation was always just around the corner.

Throw in the occasional bio-weapon scare, internet worm, Y2K, etc. there has always been something dangling over our heads that’s going to end it all.

But mostly nukes. Full-scale nuclear exchange would have been not much of a surprise had it happened.

Y2K, Climate Change (global cooling, global warming), ozone layer, Russians, Muslims, to name a few. Now go ahead and tell me why these don't count.