Rudest thing you have ever done unintentionally in abroad? Καθημερινή ζωή και έθιμα

Few years ago, when I was in Japan for first time, I was invited to a restaurant by some locals and I was served some bowl of rice. I was familiar with the use of chopsticks but not of the etiquette placing them. I simply stuck chopsticks straight into the rice at some moment, I was supposed to place them on the top of bowl. Locals stared at me for a little while and then they told me that it was something extremely rude since it is called "Tsukitate-Bashi", some act done at funerals with rice that is put into an altar. After that little explanation, I was embarrassed to the core.

Have you ever been in such an embarrassing situation?

I accidentally swore at someone when I made a gesture, which is seen as insulting. I never knew that when I made the gesture, however I didn’t regret it, as I disliked the person to whom I had made the gesture.

Great question. Being an American I've probably done some offensive things abroad but have been unaware that I was being offensive and no one felt comfortable telling me what I'd done. On the other hand I mustn't have done anything so offensive that someone had to warn me not to do it.

I experienced that Russians are super sensitive about the Gulag thing or the Stalinist period in general. As a German, I grew up being absolutelty straight forward about your ancestors crimes and we would rather want to be as open about it as possible, to redeem the countless victims pain in at least some way, by acknowledging what they've been through systematically.
In other countries it seems to be interpreted as some sort of accusation towards their nation when addressing these issues.
Oh and don't let me even start about what it is like in Turkey, when a certain Armenian topic comes up.