On a British Airways flight from LHR to AUS, there was an aircraft change that resulted in several passengers being downgraded from Premium to Economy after boarding.
Later, gate staff tried to move some of us back into Premium, but a passenger became extremely disruptive because her family had chosen to disembark rather than accept a downgrade from Business class. She then took seats that were being reassigned, as she wanted to sit together with her child, who had been separated due to the aircraft change.
The situation escalated and the crew eventually said they could not communicate with her and stepped back from resolving it.
I was surprised by how the crew handled it and felt they were reluctant to enforce instructions. In my experience on US carriers, this kind of behavior would typically result in removal from the flight. It seemed unusual that the situation was allowed to continue without stronger enforcement.