Don't be a seathog.

It's simple: if you're on a crowded bus/train/metro/subway, and the seat next to you is free, move over and let someone sit--especially if that someone is elderly or pregnant. (Even better, give up your seat for someone who is elderly or pregnant--but these days, that would take a saint.) I remember on the city bus in Oxford some years ago I watched as an older woman walked down the aisle of a crowded bus looking for a free seat. A 20-something man sat by the aisle, his backpack and notebooks spread out on the window seat. Not only did he not bother to notice her, when she asked if she could sit there, he pointed to his things and shrugged his shoulders. (I'm embarrassed to say the guy was American.) She eventually found a seat elsewhere, but I was pretty much ready to give that kid a flogging (with the whip I carry in my purse particularly for such occasions).

For some reason, I don't think this sort of thing would have happened 70 years ago.