Each country has their own tradition and cultures. Therefore each country has some eye-popping social cues that probably won't pass in your home country.
"In Orthodox Jewish weddings, there's a tradition that directly after the ceremony (like between the ceremony and the reception), the bride and groom go into a special room for 'Yichud' (togetherness behind closed doors between a man and a woman alone, which is forbidden unless you're married). The assumption is that they bang (which, traditionally and among practicing Orthodox people, would be the first time that happens), and then they just come out and dance with their friends/family, with everyone holding the knowledge that ostensibly they just f**ked."
"In the UK, if a waitress or waiter drops a plate, or smashes a glass in a restaurant, at least one person (and often many people) in the restaurant will shout WHEEEYYYYYYYYY. In effect, deliberately highlighting their mistake with a loud, sarcastic jeer. It's really not clear why this happens, but just does, and I don't think it would be acceptable in most other countries."
"Korean (Canadian) here: it is poor taste to not appropriately address someone by a title like 'big sister', or 'auntie'. While auntie has more respect than big sister, calling someone auntie instead of big sister is not great either. When I was in my mid 20s I had Korean neighbors down the hall from me in my apartment complex; a young couple with cute little boy. He would get restless and want to walk up and down the halls with his mom at least once a day. One day, I say hello to his mom and she told her son to say hi. He bowed a little and said 'Hi Auntie' ('Ajumma'). Our jaws dropped and his mom immediately started correcting him to say 'Big Sister' ('Noona' is a big sister to a boy). He looked at me and continued to call me auntie, while his mom was apologizing to me for not calling me 'Big Sister'. That was the day when I realized I wasn't young anymore and to accept the fact that I will be called 'Ajumma' instead of 'Noona' or 'Unni' (big sister to a girl).
"In Hungarian weddings, around midnight (of an all night party) the bride and groom will disappear, and then reappear some time later with the bride having changed from her white dress into a red one. Then the wedding emcee will basically announce that there is one less girl in the world and one more woman, and essentially now that she's no longer a girl she can dance with anyone... for money. Then the wedding guests basically put money in a hat to have a brief time to dance with the bride, and if you put a lot of money in you can even request the song. (At traditional, huge weddings this would even go on so long that groomsmen would show up wearing drag to 'pretend' to be the bride and give the poor woman a break!) Mind, even though it's perfectly normal to live with your boyfriend/girlfriend in Hungary these days before getting married, and it would be weird to not have sex beforehand, I can't say I have ever heard of other modern cultures celebrating the consummation of the wedding short of nomadic tribesor similar."
"In Asia, Living with parents when you're the sole earner and supporting the whole family in a house bought by your own money. Because in my country (& culture), parents support kids till they get a job, then its kids' responsibility to support parents."
"I used to have my haircut by a woman who is Vietnamese. There was a new stylist at the shop, and Minh (my stylist) was fretting about having been very rude to her by accident. She said she had been addressing her as someone her own age, instead of something akin to 'Auntie' (the new woman was older). I said that most women consider it a compliment to be mistaken as younger than they are, but Minh felt very bad and was slinking around all apologetically, that day. TDIL (That Day I Learned)."
"When I moved to England three years ago, this was very odd for me in the beginning. All my colleagues were like 'Alright?' every time they see me, even multiple times a day. At first I find it a little annoying but as time goes by I started to like it. People acknowledging you even though they don't mean it, it's still better than passing by in silence pretending that is not another human being walking towards you, like in my country."
"My professor taught in Japan. He spoke of his time there a lot. Some of this might not be true as its a second hand story, but still. In Japan it's impolite and childish to expect to be able to tell a chef 'no tomato please' or 'no onions' or anything like that. If you want food without onions you should order something that doesn't contain onions. You can pick the onions off but people find that childish too. Even though he lived there for seven years he was still described as 'that foreigner'. Even by his close friends or neighbors. Assimilation into their culture is nigh impossible, they'd prefer you to conform to their idea of an American foreigner. Walk around not knowing where you're going while wearing a USA baseball cap and eating a hot dog. Also, apparently it's incredibly insulting to use your hand the classic 'come hither' motion. Palms facing up and waving your fingers towards yourself. That is something you'd do to a dog. You're supposed to have your palm facing the groundin Japan."
"Not actually from this country, but a friend from South Korea said that asking someone's age is one of the first things you do when meeting them (so you know how formally to speak with them). Logically, it makes sense, but I can't imagine walking up to a woman/man I've never met here (Canada) and asking how old they are. It'd be awfully rude."
"To greet any person with a kiss in the cheek. I live in Argentina and we even had a guy in our subreddit a few days ago asking if her girlfriend was cheating on him because a friend gave her a kiss in front of him. It would be awkward to greet a woman or a male friend with anything else than a kiss in the cheek here."
"We do this in Canada. I would feel super rude if I sat in the back seat of a cab when it was just me. Actually, even in a group there's usually one person delegated as the 'front seat person'. The front seat person handles the payment and makes small talk with the cab driver. This isn't normalelsewhere?"
"I lived in Korea for three years, and once I learned the language, I found out people were saying terrible things about me everywhere I went. When I would confront them, they would be shocked that I understood them, but never apologize. In fact, some of them would be angry that I was able to understand and talk to them as if a language isn't something that you can learn."
"I learned this sadly in Chile. Inviting your family, friends, co workers, neighbors, the lady who cleans your parents house, her family, the bus driver, that person you met three years ago at a indigenous people issues seminar and his wife to an 'asado' (bbq) at your place and really mean it and expect everyone will show up."
"Went on an orchestra trip to France as a kid. Did home stays. Was definitely given wine. After convincing this woman we shouldn't really be having wine, she says ok..have some cider then. After realizing that was alcoholic too, we just gave up and went with it."
"Here in the USA, I'm just now finding out that we're the only country that says a Pledge of Allegiance to their flag, and many other countries find that strange. I'm not sure if that counts or not. I never thought anything of it in school. I just listened to the person on the loudspeaker said it, and never really said it myself."