I swim one morning a week at the YMCA. There are 6 lanes at the pool, and nearly 100% of the time, you are required to share a lane with another person. Since not all people (myself included) grew up swimming on a team, not everyone knows that there is a set of etiquette guidelines that swimmers should follow. Luckily, because the YMCA is a public place with many users, these Lane Etiquette Rules are posted on the walls. They are simple, common sense things that include: Alert swimmers that you are joining their lane, Keep to one side of the lane, If you have to circle swim choose a lane with swimmers of your own ability... etc. Most of these things are so obvious, and on top of that, posted on the wall, that I get very annoyed when these guidelines are not followed.
As an example, proper etiquette dictates that you let any swimmers already in the lane know that you will be joining them. Last week I was swimming and as I was approaching the wall in the deep end to do a flip turn, someone jumped into my lane, practically on top of me. First of all, I was going to be on my way in approx 3 seconds. Your jump seriously couldn't wait?! Secondly, it totally freaked me out because I certainly did not expect someone to jump on top of me. It startled me and in a pool that can be dangerous. Letting swimmers already in the lane know you are joining in is as easy as putting your legs over the edge of the pool while the person approaches the wall. They just need to be aware of your presence prior to you sneaking up on them; you don't need to jump on top of them or stop them for a chitchat. A few weeks ago there was an old woman who just started swimming in the lane I was sharing with another swimmer. She didn't say anything, she just started swimming. (And I use the term swimming very lightly because it was more like floating with slight arm movements. I think she was averaging about 4min per 50yds if not slower.) The other woman in my lane nearly swam into her, and I wound up having to move since the old lady refused to comprehend what we were trying to explain to her.
Another pool rule is to circle swim when there are more than 2 people in a lane. (For you non-swimmers, that means people swim counter-clockwise, always staying to the right as you swim as opposed staying on one half of the lane as you would do when having only 2 people in the lane.) Although I see the necessity, I very much dislike it, mostly because it is impossible to find lanes with people of equal ability. Someone is always faster than the others. At the YMCA, since most of the people in the pool are over 60, I tend to be the faster one. There are times when I'm not, and I always make sure to check where the other swimmers are to know when to yield at the wall. It is proper etiquette to yield to a faster swimmer when they are close behind you. The faster swimmer can signal this by tapping the person's foot, which means that the slower person stops at the next wall to allow the faster swimmer to pass. I usually notice when someone is closing in, and yield automatically, probably because I have a heightened awareness of the problem. Usually, I wind up having to sprint passed people because they never yield. So frustrating, especially when you are trying to do fast sets.
There is also a rule about how you should actually be swimming laps in the lane. There is a woman who "swims" around the same time I do in the mornings. She takes the water dumbbells, stands in the shallow end, and does some kind of water aerobics. The YMCA I belong to has a special therapy pool for this purpose. It's about 4ft deep and perfect if you're not actually doing laps. So why this woman insists on taking up space in a lap lane is beyond me. Although, she usually shares a lane with super slow old lady that I mentioned above. Maybe they are BFFs.
This isn't one of the posted rules but it annoys me anyway, I hate when people swim breaststroke or butterfly in a shared lane. These strokes require a wide berth and are very disruptive to the person with whom you are sharing a lane. I have seen experienced swimmers switch to freestyle or one-armed butterfly while their lane-mate swims by; this is acceptable. It is not okay to smack the other person every 25 yards. Please, wait until you have your own lane or at least be aware of the other swimmer so you can adjust your stroke accordingly.
I am also annoyed when people do not swim straight. I have crashed into a few people because they strayed over the line and into my half of the lane. Do you know how much a literal head-on collision hurts? A lot. It also hurts to clonk hands or get kicked, so if you go to the pool, stay on your own side. And if you're going to cut across a lane (for example, if you are trying to get to the stairs) make sure the swimmers in the lane aren't approaching. I nearly killed a woman a few months ago when I got to the wall in the middle of a set and nearly plowed into her. I mean, really. You must have seen me coming. Did you think I was just going to stop halfway through that lap??
Finally, don't dirty the pool up. That means, take a shower before entering to wash off the sweat, lotion, deodorant, etc. Wear a swim cap if you have hair in order to prevent nasty hair balls that float around. And never, ever ever pee in the pool. Seriously.