I hate the demand for a smile, too. How can you know what's going on in a person's life? Most people don't grin like an idiot all the time anyway, but I was on the subway once, I just found out my family's dog had died earlier that day. I was trying to keep it together, and some guy with a shit-eating grin leaned…

Sure, I tell cashiers and receptionists have a nice day all the time, because . But it's New York, not a small town where you say hi or nod to everyone you pass. Telling a total stranger to have a nice day is not a thing people do in large cities, unless you have a motive.