being asked to smile?

I don't smile a lot, naturally, and occasionally strangers will cajole me to smile. This happens in stores, at gas stations or bus stops and other such places where I'm not actually meeting a person. I used to favor them with cold glares or looks of puzzlement, as it felt quite intrusive, but these days I might laugh briefly. I thought this was friendliness or a criticism of my lack of sufficient politeness. But after reading a recent post I wonder if this is sexist behavior. I honestly can't remember whether it came mostly from men, though it generally has been from people obviously older than myself.

So, is it? Care to jot down a quick comment of
1) whether/how much you've been asked to smile by strangers and
2) what gender you present?

It'd be fun going around telling people to smile, though it's California where they do so freakishly often. This merits further investigation. Then again, so does my math homework.