What's your "rules teach horror story"?

I put a lot of effort into learning and teaching so I'm always mildly horrified at how lackadaisical people get when it comes to teaching. I once had someone opening the Hansa Teutonica rulebook and going "Page 1. Set up." I literally thought it was a joke but no, they were going to read the book to us cover to cover.

Another time someone taught Beyond the Sun by basically saying "It's easy, you just go here to trigger the actions and then it's area majority over here, you'll figure it out as we go, you can start."

It got me wondering, what's the worst experience of teaching/learning you've had?