that video went viral, but in honesty, I am not sure it was a stealth flip-off.
When I was in 6th grade, we had a teacher from england in an exchange program. He had no idea what an elevated middle finger meant. As soon as we discerned that, every time someone raised their hand to answer a question in class, the finger went up, he would call on them to a giggly titter, no one ever did tell him that I remember. I have not been to the UK so I don't know if it is now a "thing" there.