This whole thing surrounding "never tell a woman to smile" is such a joke but it has gotten to the point where some women think they can be downright rude and grumpy when working in the service industry.

Look, if your job is to serve people food, or to deal with customer complaints, or any type of customer interaction, then you should leave your problems at home and treat the customer with respect. And if you act like a rude self entitled jerk as a server, then don't expect a tip. There are plenty of jobs out there for people who are grumps, heck I used to work in trades and people were miserable there all the time, but at least you werent being miserable to customers.

If I was an employer and my employee wasnt being kind to my customers, its amazing that the notion that you should "never tell a woman to smile" would mean that I would probably get cancelled for canning her grumpy ass.