Interesting that these all seem to be "personal space" issues!
Here's one I experienced a few years ago: The pool I belong to has umbrellas for everyone's use. Once someone has set up under an umbrella, it's considered taken. It's usually one family per umbrella, or perhaps a couple moms who came together, and their kids. Sometimes a couple families arriving together may share one of the larger ones (in years when there have been larger ones). Sometimes a friend arriving later is invited to share the umbrella space. But in general, it's one family per umbrella and you only share if you arrived together or were invited to join someone.
So imagine my surprise one day when I glanced over and saw someone I didn't know sitting at the very edge of the shade cast by "our" umbrella. She was not there when we arrived, and must have slipped in while I was busy putting sunscreen on kids and reminding them of ground rules for being at the pool, etc. OK, I didn't exactly "own" that shade, but it felt very odd. Especially since she never said "hello" or asked to share our shade. It almost appeared like she was trying to ignore us in hopes that it would make her invisible or something. Very odd. I couldn't tell if this was rude, just odd, or just that I have an exaggerated idea of how large my personal space bubble is and I need to get over it.
But then it got weirder. As the day wore on and the shade moved (and got smaller), she moved. She never moved when I was looking, but there was no denying that she was edging ever closer to me. At the rate she was going, she was going to end up in my lap! I was beginning to not just be annoyed, but worry that we'd run out of shade. One of my daughters is in a wheelchair, and I need enough shade to keep her chair shaded and enough for her to stretch out on the ground on a towel sometimes too. I didn't want to come back from taking her for a swim and not have enough space in the shade.
I have no idea why I didn't say anything, except that I don't know what I would have said. When she first arrived, I was kind of thrown off balance. And the shade was certainly big enough at first, so I guess I worried that I would be the rude one if I said anything. And as time wore on, the longer I didn't say anything, the harder it got to say anything! Very silly, I know.
I finally caught her in the act of moving, and managed to catch her eye. "I'm watching my grandchildren, I have to stay out of the sun," she said. "Uh huh," I answered. "I have to keep her out of the sun, too," I said, indicating my daughter in her wheelchair. She said nothing more, and went back to reading her magazine. I rearranged some of our things to mark our territory, and when my chair was no longer in the shade, left it there as a barrier, figuring she wouldn't be so bold as to actually climb over our stuff to get to our shade. (And actually, I often leave my chair in the sun anyway, since my daughter needs the shade more than I do. I also tend to rearrange our things to follow "our" shade, so what I did wasn't all that different from what I usually do.)
Eventually, she left. She never camped out in "my" shade again, although I did see her do it to other people. I have no idea if other people were bothered by it, or if I'm just more prickly than the average person over personal space issues. I do wonder, though, why she didn't just sit under one of the pavilions when there were no free umbrellas, if shade was so important to her.