There are two forms to the "smile" question. There is the passive/aggressive form that is non-sexual. Examples are:
"Cheer up mate, it could be worse."
"Give us a smile. You might even feel better."
"What's up love, lost a quid and found 10p?"
Then there is the sexist version:
"You would look quite pretty if you smiled."
"A smile would make you really sexy."
I don't think that the second set of examples are ever directed at men.