OK, I got another one!!!
It doesn't really bother me, but it does kinda makes me a little sad: When you see and connect, albeit passively, with a family. Then as you look around, you notice that their vacation is over and they went home. To me, when you first start out on the bus going to a park, you are all wide-eyed and bushy-tailed. And you are cracking jokes on the bus and having fun with people. And you tend to see some of the same people at the resort or on the buses. You have that small talk and you wave.
Then after a while, you notice that you don't see those people anymore. And by the end of your trip, you notice that no one looks familiar anymore. And you have a whole new crew of people at the resorts and buses. Then you know that it's time to go.

And you also become 'That Guy' on the bus.
You know 'That Guy': When on that first day riding the bus, you crack a funny joke and everyone laughs. And 'That Guy' laughs too, but not as much as everyone else. They have that knowing smile when they look at you. And they are hugging their children a little tighter than everyone else and whispering in their kids' ears, like they are trying to get them to remember and cherish this one particular moment. And when you ask 'That Guy' how long they will be at WDW, they always say "It's their last day", or "We leave tomorrow morning."
Yeah, when it's time to go, I become 'That Guy.' I look sentimental in my face. I talk to the kids like "Remember when we...?" Or we just smile knowingly at people as they come on all wide-eyed and bushy-tailed.