I'd like to know if the airlines offer guidelines or training on, for lack of a better term, mood control for FA's. Some flights we get one who can smile and be pleasant no matter what the previous pax said to her, and sometimes we get others who arrive at the airport in a foul mood and want to make sure every single pax knows about it.

I once worked for a manager who said "I don't give a d@mn about your problems; when you're at work, smile at every customer." and the staff who worked for her had a pretty high standard of customer service. (not great morale, but that's another issue)

In this day of unions, do airlines, who used to do girdle checks and weigh-ins for FA's, dare tell the staff to smile? Give guidelines/advice on ways to temper your interaction with customers when you're personally stressed? Yes, I know FA's are human and everyone is different, but are there interaction guidelines?

This isn't a security question, it's a customer service question.