Am fascinated by how different countries - cities even - have different social rules that are unspoken but nonetheless most people adhere to. For example, in Japan when you take or give an item to another person you do so with both hands, not usually one. You also are very careful not to say “no” or reject something/someone in a very direct manner as this may cause offence.
London - generally I observe Londoners to be very polite, but they do not initiate conversation. There is a respectful sort of quietness on the trains; no talking whilst travelling seems to be a social rule of politeness.
France - careful to abide by the rules, say, of the swimming pool or in other public spaces and maintain a uniform behaviour in public. Outrageous or ribald behaviour unless it’s part of an organised group having scheduled fun is frowned upon & strangers will pick you up on it if you step out of the social line very quickly. Same goes for Switzerland.
What have you observed and where?