I had the radar on and saw everything he was going to do before he did it. I eased on the brakes, weaved onto the curb and avoided being hit by him. I honked (first time I've ever done that) and raised a hand in wonder at his cluelessness. The guy in the cage jumped when I honked, then made a point of ignoring me when I gestured. I frightened him by honking, he was happy to knock me off the highway and then ignore the consequences.
I'm surprised at how not-angry I was. Even though this clueless old git had no idea what was happening around him I couldn't get angry with him. Like so many other caged drivers he is in his own world, remote from the consequences of his ignorance; happy to thump down the road at 90 kms/hr without knowing what is going on around him.
After shaking my head I was back in radar mode, wondering what the next cage driver would do. Riding is only really dangerous when you're doing it with a lot of other human beings.
I got to the dentists and had a nice chat with my hygienist who rides. The ride home was without any such drama, but I'm left wondering how often cage drivers think about what's around them.