This question is interesting in that under normal circumstances where things remain in my own control I won’t ever get bored. I can find things to occupy my time and have zero problem having times where I just sit and do nothing as a way to relax.
On the other hand, certain books, types of conversations, and obligatory events are a different subset of situations altogether.
In a book, the fastest way for me to be bored is for there to be no tension. When the story doesn’t exist but as a conduit to describe, describe, describe with no direction. When there’s dialogue that goes round and round but never gets anywhere or only repeats tired ideas that are decidedly lacking in wit, yet the characters are thinking themselves witty. Another way for me to have the potential to become bored is when there’s too many jumps, usually in characters, where I’m forced to essentially “restart” the process of becoming interested because all that came before has suddenly disappeared.
In conversations, the way to get me bored isn’t to monopolize the topic, though that can get old after awhile, I usually like seeing the passion other people exhibit when they’re talking about something they love. It’s when my words are dismissed unilaterally, my opinions considered irrelevant and any attempts I make at being part of the conversation thrown out. Interrupting me constantly will also make me check out of the conversation. If you indicate that you have so little regard for me and just want to monologue, then why not talk to a wall?
As for obligatory events…this is when it would be rude for me to pull out a book to fill the time, leading to me to sitting up straight and doing my best to pay attention, to be polite, because if I’m there it’s because I must care and I’ll do my best to show it. That doesn’t mean I’m not bored sitting in the middle of the wedding attendees where no one can hear the bride and groom exchange their vows and so we just sit there and pretend we’re not bored. It happens.
Luckily, I’m not one to get bored normally. I have a TBR list a mile long and most of the books are sitting over my head right now. If I’ve got nothing to write, nothing to edit or nothing to do otherwise, I’ll always have something to read.