Perhaps if a third party, not involved in the incident, goes up to talk to the driver and tell them they had just endangered someone, it would be better received. There were 2 or 3 times when a bus or taxi almost swiped me, and some other (more outspoken) cyclist approached the driver a the red light and told them to be more careful. So maybe, even if we don't speak up for ourselves in an incident, we can speak for others when we see it happening.