Not sure if call it "startling" but I did witness an exchange once on a bus they was very unexpected.
When I was commuting to downtown Denver for work I took the bus. My usual routine was to get on, sit down and pull out a book to read while waiting for the rest of the passengers to board. One day there were two Asian men in suits who decided to stand in the aisle rather than sit down in any of the open seats. This was not too unusual as the buses were usually full enough at that time of day that people ended up standing as the seats were all taken. Some people just opted to stand as they would likely end up giving their seat to someone else anyway.
However, on this day these two men weren't simply standing while waiting for other passengers to board, they were standing in the way of passengers trying to get to the empty seats in the back of the bus. I saw this and thought it was quite rude to simply stand there and block others.
A woman politely said "excuse me" as she approached them but they didn't move or even appear to notice. In a slightly louder voice with firmer tone she repeated "Excuse Me" and added "Can I get past you?" This time the men did seem to hear her as they turned, gave her a look then went back to their conversation which I couldn't understand as it was in an Asian language that I don't speak. From where I was sitting they looked more annoyed by her request than anything.
At this point I put my book away and stood up to go confront these two. My intent was to go into Army Sergeant mode and ask them to move in a tone that they would understand that I wasn't really asking.
I quickly saw that I wasn't alone as two other gentleman had stood up at the same time I did and were looking right at these two also. One was a white guy, a bit bigger than me and dressed in a manner that looked like he worked a blue collar job. The other looked like a college student, he was a black kid dressed a bit like Will Smith in the Fresh Prince tv show and had been listening to music through these overly large headphones that looked like what a DJ at a club would wear. The kid was the smallest of us three but also the closest. Me and Blue Collar stood where we were and let the kid go first. I'm not sure what the other guy was thinking but I was expecting these two to blow off the kid the same way they did the woman so I was still ready to move in if needed.
What I was definitely not expecting was this kid to start speaking to these guys in the same foreign language they were speaking. They turned and said something back to him to which he replied by motioning to the rest of the bus then pointing at them and said something in a tone that sounded like he was scolding children. The two men lowered their heads and hurried to the very back of the bus. The kid then turned to the woman, apologized to her then sat back down and put his headphones back on.
Of all the people on the bus that day that kid was not the one I was expecting to hear speak in fluent, I'm guessing Cantonese.