It's just a long winded 'smile' isn't it. Telling a stranger what to do with their face is really insulting. Can't believe the responses. Best skit ever on this.
DH actually had a senior (clearly very strange) colleague tell him to 'smile' the other day. He came home really pissed off and said something along the lines of 'Something happened to me today that I think normally only happens to women and it was really, really annoying'. Also very unprofessional in a work context. I was somewhat cheered that it doesn't only ever happen to women (is that wrong?!).