LOL. Isn't that the truth! Definitely not eavesdropping. My wife and I said several times to each other while we were there that we'd be surprised if our neighbours heard one word we said. I'm willing to tolerate some "kid noise" (I think I was one once) but when it gets out of hand I don't mind letting them know. btw - these people were a good 150 away from us!
Another pet peeve comes to mind ... how does one manage to set off their car alarm when they're camping? I once heard a guy, not the guilty party, shout out ... "there's better ways to scare off the bears." ha ha.
I'll admit, this happened to me a few weeks ago in Colorado. We were camping off of Last Dollar Road and I had my keys in my pocket. Somehow, the way I was sitting caused the panic button to be hit, and off goes the factory alarm (horn). It was the first time it had happened and unlike previous vehicles I had, hitting the unlock button doesn't shut it off. Nor does any button, in fact, I had to start the engine for it to stop! It was only about 15 seconds but it seemed like an eternity and I felt awful. Luckily there was only one other group in ear shot, and it was just after dusk, so I'm sure nobody was sleeping.
As for mine..
1. People being very loud, as others have said, is the primary
Particularly those with kids that don't even attempt to keep them quiet. I don't expect zero noise or anything, but also don't expect them to be running through the campground, through others campsites, screaming at the top of their lungs. One of the first things we taught our kids was to be respectful of the peace and quiet many campers are seeking. BTW, I will clarify, day use / swimming areas / playgrounds, I couldn't care less if they're loud. This is one of the main reasons we only camp in campgrounds, if absolutely necessary.
2. People building multiple fire pits in a single back-country campsite
I have started seeing more and more of this on BLM land, in sites where we have camped repeatedly over the years.. One, that had a single large pit for years, got all the way up to 5 separate rings one year! I always disperse / deconstruct the extras, and cover them well enough so they can't be identified. I have found some that were less than 10' away from the primary.. I guess the 'view' wasn't exactly tailored to their specific setup? :/
3. Strangers camping close to you in the back-country
There's a reason I drove 45 minutes from town up this mountain, on a 4x4 trail, and it wasn't so I could have 'neighbors'. If I can see or hear you, you're too close (with some obvious exceptions). If there are no other previously used sites or something, I am way more willing to tolerate it, but I have legitimately had this happen when there were dozens of open sites that they passed, to camp closer to me than if we were in a state park. I don't know if they're just scared to be alone or what!