or worse when you realize someone you were joking with was actually being completely serious

I liked the stories about the moon landing not happening for many years (I'm 58), not because I believe it didn't happen, but because I loved looking into what would have to happen to cover it up and how impossible it would be to cover it up. It was a joke until I realised that people were starting to take it seriously. Alternative history was a hobby I was into, I was writing (terrible) stories myself and then they turned everything into "alternative facts" and made up history and took it for real and I just had to give up the hobby completely. It is no fun to write or read a story about a flat earth or people living inside the globe or aliens when you know someone actually believes it to be true. That's why we can't have nice things:

like half the worlds gone insane