#3. Standing in the Wrong Place
There aren't many great places to stand on a bus or train; by the time you're forced to stand, the thing's going to be packed enough that no matter where you position yourself, you'll be in someone's way. The only thing you can do is minimize the number of people you're inconveniencing with your big standing ass. And there are a few simple rules for doing that:
1) Don't Stand in Front of the Doors
If you're nowhere near your stop, you should be nowhere near the door. The back of the bus or the middle of the train car are best. Unless it's packed, and the doors are the only place where there's the three cubic feet you can squeeze yourself into, in which case, fine, stand by the doors. But just know that you're going to be getting on and off to make room at every stop.
2) Don't Lean on Poles
Those poles are for multiple people to grab on to, necessary for keeping buses from becoming mosh pits/American Gladiator events. When you lean on or hug one of these poles, your back and ass are taking up valuable grabbing space. According to Transit Law, anyone who sees you doing this is allowed to grab on to you for support. The arm, lapels, neck, whatever.
Or the funhose.
3) Also the Escalator. Don't Fuck Up the Escalator.
And for the love of Escalating Jesus, don't stand on the walking side of the escalator. (The exact side varies by country.) You're going to get yelled at, or stepped on, or shanked in the neck. In the future, escalator steps will be able to detect when someone is standing on the wrong side, and will fall out beneath that person, dumping them into pits of ... something futurey. Let's say nanolava.
(On a side note, this advice evidently doesn't apply in Japan, where some cities have started banning walking on escalators. Having a mix of walkers and standers increases the risk of collisions, and a standing-only escalator policy evidently improves throughput. This is interesting science, but I urge you not to try this shit anywhere else in the world if your neck is vulnerable to shankings.)
#2. Waving Bags Around
Having a bag at all on mass transit is already a pretty big nuisance for everyone, so if you can avoid it, please do. But I get that you've got a meeting, or a class, or a shitty hostel to get to, and you'll need some stuff when you get there.
There's a Lonely Planet guide to Belgium and a really filthy sleeping bag stuffed in there.
The problem with baggage is pretty obvious: It takes up space. Space that could be used by other people, or worse, space that is already being used by other people. When you hit someone with your bag, you are committing a hate crime, one that's been perpetrated by the bag-having against the bagless for too fucking long. A day is coming, sooner than you think, where everyone who doesn't put their backpack at their feet on a crowded train is going to be put against a wall and shot.
The children will be encouraged to frolic in their blood.
#1. Talking to People
This is the biggest violation of bus etiquette possible, because the violators are no longer putting their physical presence in someone's face. They're putting their words there.* It's possible to ignore someone standing like a dick in front of the doors or swinging a backpack around like a wrecking ball. But ignoring someone talking at you is impossible. The words can't not be heard, can't not be understood, and before you know it, some asshole's inane thoughts are rattling around your brain without your permission.
"The rain's pretty wet today. This bus driver sure likes to make right turns. Brain medication tastes like vowels."
Every time I see this on the bus, my toes curl. It is dragging-a-cat-across-a-chalkboard excruciating for me to listen to someone else's awkward, kind of creepy small talk. Even when it's not me getting talked at. I've gotten off buses several blocks from where I need to be to escape a one-sided conversation about rain dampness that I wasn't even involved in.
Understand that I'm not making a full-throated defense of being shy or isolated. I am all in favor of meeting and talking to strangers in other settings -- at parties, at the bar, at the sex club. Those are appropriate venues, because everyone involved (presumably) wants to be there.
WHICH IS NOT THE CASE ON THE GODDAMNED BUS.
"My day went fine, young lady. It always went fine. That means I don't want to say anything more about it. I don't know you. No, I don't remember you from the club. The fuck room doesn't have lights on for a reason. Oh look, it's my stop."
*Triple there combo!