I don't think about etiquette much, but I've had occasion to a couple of times recently.
The first was at a bar where my husband Rob and I are regulars. It was crowded, and the only seats were in the corner. We didn't want to be jammed against the wall, so we left one stool open. So there was an empty stool to our left and an empty stool to our right. An older couple came over, clearly looking to sit down. We immediately shifted, so that there were two seats together for them.The woman thanked us, and I said something along the lines of "Just simple bar etiquette."
The other occasion was at the outdoor lap pool of the athletic club we belong to. That pool is always in high demand, and Rob and I always share a lane, even if there are others open. On a recent beautiful sunny day, as we were contentedly going through our respective exercise routines, I saw two women---one youngish, one middle-aged---jump in the lane that was being used for little-kid swim lessons. I thought to myself, "What the hell?" (or something like that).
Sure enough, the lifeguard/instructor said, "Can you please move to another lane? I need to keep this lane open for the kids." The women managed to look both annoyed and confused and moved to the next lane, which was next to Rob's and mine. Problem was, there was already a guy swimming in that lane. I heard Youngish say to him, "Are we interfering with your swimming?" He answered that yes, indeed they were.
So now the two women and I are at the same end of the pool, just a foot or two away from each other. I'm doing the part of my routine I call the Stomp, 140 really fast walking-in-place steps. I hear Youngish say to Middle-Aged, "We could move to the next lane. They're just paddling around like us." Hugely offended and annoyed, I said, "We're not paddling around. We're exercising. And there's already two of us in this lane. We always share, to be polite." (I'm not sure why I included that last piece.)
"Oh," Youngish said. "I don't know the etiquette of sharing lanes here."
I said, "The etiquette is you have to ask and be invited in. It's like with vampires."
It was at this point I realized that Youngish is unfamiliar with vampire-related pop culture, because she looks at me blankly. I tried to explain: "Vampires can't come into your house unless you invite them in." Now she apparently thinks I am calling her a vampire and looks at me as if she wants me to drown at that very moment.
"I'm not calling you a vampire," I said, realizing that this conversation has become absurd. "It's a pop culture and literary reference." She gives me a look that is both vacant and full of hate. "Bram Stoker," I added, knowing it will not help.
Fortunately, Rob and I were close to the end of our routines and I told Youngish and Middle-Aged that they could have the lane in a few minutes. Youngish said "No problem" as if I was apologizing for something, which further irked me.
There is no great lesson or revelation in all of this. But I have imagined Youngish and Middle-Aged coming into the bar where Rob and I had automatically shifted our seats. They look around, see no vacant stools, but plop themselves down anyway, in the laps of the current occupants. And seem amazed when they are met with cries of indignation.