Excuse me, but did you actually have the audacity to imply in your 'moment of clarity' that because 'city dwellers' were giving this man the time of day that it induced a 'time of existence' for him? Of all the pompous, self-aggrandizing ideas. That man has an existence, believe it or not, OUTSIDE THAT CHECKOUT LINE regardless of whether you deign to see it.

This time was probably the first time in weeks he was interacting with people on a personal level and not asking them for change. So naturally, despite being involved in an argument, he wanted to continue this interaction and exchange of words as long as possible.
PLEASE! Do you honestly think that because this man is homeless that he has no personal life? He panhandles... that's how he gets by. He has friends with whom he can enjoy an exchange of words. He has a place to crash. He has a corner. He has a favorite beer... Seems to me that you've dehumanized him more than someone who just ignored him... you've pitied him and placed him in your idea of his world where his only 'time of existence' is in your checkout line.