The young guy was looking for trouble. The old guy even got up and moved away from him - and the old guy seemed to mostly be joking until he did that - and still the young guy went after him. Stable or not, that is about the way you have to handle someone coming at you when you have no real escape at that point. The young guy messed with the bull and he got the horns. Of course, this came long after the threshold that any smart person would stop at: do not engage loud/crazy people on public transit at all, better to just nod and smile and not keep their attention long enough for them to decide to make you a target.