I would have answered “why don’t you shut your fucking mouth before I stuff your old ass in that envelope receptacle.”
Of course, I would have also said that if he has said “good morning”. I don’t like strangers striking up a conversation with me.
I had a similar experience recently.
I’m more worried about antisemitic, racist, or homophobic scumbags who can figure out how to work things like ATMs and bank accounts than I am about the other kind.
Still, it’s fun to think of all the things one *could *have said to the old racist.