Here's an easier exercise, reverse the rolesImagine a cashier doing this randomly at a grocery store.
Imagine a waitress randomly doing this to someone at a restaurant.
Imagine a theater usher doing this to a random person at a movie theater.
Imagine a doctor doing this to a random patient.
Imagine telling anyone "you're ugly" unless you're really familiar with them and sure they'll take it as a joke.
This is unprofessional and an appropriate reason for firing. It's also just rude and mean. Lady needs to go think about life.