My pet peeves boil down to a lack of consideration from other guests. For example: flash photography on dark rides! It completely throws me out of the experience, and it's just so visually jarring.
But one of the biggest ones for me is people stopping in the middle of the row in various shows. The CM will tell everyone to "move all the way down" and they just ignore the instructions and everyone has to climb over them. It's inconsiderate and essentially saying that they don't care about anyone else's experiences but their own, that they deserve the best seats, even though it should mostly just come down to luck.
I have so many others, but those are the two things that really raise my blood pressure. (The cutting in front for parades/fireworks used to be a big one, but I've avoided that frustration by not queuing up anymore. I accept a worse view in exchange for not getting angry/defensive over the spot I waited an hour for and then a huge family tries to push me out of the way. It just makes me happier to not have to deal with that confrontation.)
I'm trying to teach y kids to think of other people nd be mindful and respectful of them... You would not be surprised how many other people are not teaching this to their children.