How many lines of work are there in which customers are sometimes actually offended if you stop grinning for a while? ...And feel they have a right, or even a duty, to comment on your facial expression, apparent mood?
I worked in a shop recently and was informed endlessly that I "looked tired". ("I didn't feel it until you became the 150th person today to pass on that titbit".) I find it odd. Would you go to a solicitor or a surgeon, tell them they looked tired and ask what they were up to last night?
I couldn't help finding something a teeny bit patronising about it all. It was one of the reasons I quit.