One of the most boring experiences I've had was a three-day training course I had to attend for my job at a bank in Colombo, Sri Lanka, about two years ago. It was about new compliance regulations, and it took place in a windowless conference room at the head office.
The trainer was a very pleasant man, but he read every single slide aloud, word for word, in the same flat voice. There were about two hundred slides per day, full of tiny text. We weren't allowed to use our phones, and the air conditioning was set so low that everyone was wrapped in their jackets. By the middle of the first afternoon, I could see people's heads dropping.
I think I felt bored for two reasons. First, there was no interaction; we weren't asked a single question for hours. And second, I couldn't see how much of it related to my actual daily work, so my mind kept wandering.
To cope, I tried a few things. At first I just doodled in my notebook, which didn't help much. Then I started a private game: I tried to turn each section into a real situation that might happen at my branch, and I wrote a short example for each one. That kept my brain active, and, surprisingly, I ended up remembering much more than most of my colleagues. On the last day I offered to share my examples with the group, and the trainer asked if he could use them in future courses. So, oddly enough, something good came out of the boredom.