You have a point there Sophia, apart from those people who have had it in the past or have taken the time to learn about it. My old T used to say that a lot of people don't know the difference between being temporarily "down in the dumps," being a little sad because something happened, and being depressed. Maybe that's part of the reason it's so annoying when someone says "smile!" They don't know what a loaded request it is. Still, even if I was just having a bad day it doesn't make sense. Kind of like someone telling me my feelings aren't good enough.
However, one thing I never thought of is maybe that person is being triggered into a place where it is intolerable to see someone else having a bad day. Always complicated - lol.