Got a few that come to mind:

Three young guys, I would guess in their early twenties, were being obnoxious in a silence compartment. Other people noticed but nobody went beyond casting disapproving looks. One of the boys defiantly started asking the other passengers one by one if they found the boys annoying. The first few people cowardly denied annoyance until one of them simply and firmly responded ‘yes’. The boys had not expected this and just packed up and left. It was hilarious to see their faces, they had not expected that haha

In Spain, a ticket inspector addressed me in Spanish, which I don’t speak. I tried communicating in English. Unfortunately the ticket inspector thought that I would magically start understanding Spanish if he increased his speaking volume. After a few rounds of this he was practically shouting at me. Luckily at that point another passenger joined in to translate and we managed to sort things out.

On the train from London to Edinburgh, an obligatory drunk randomly shouting Scotsman