This is why I am so happy I don't work in retail anymore and will gladly step in and say something to someone when I see them being a dick to an employee.

I cried in the backroom many a time during my retail career due to people yelling at me for things outside my control. Eventually I just started crying right in front of the customer and that at least generally made them realize they were being dicks.

Partially unrelated but last week I was at a movie, accidentally spilled my popcorn and I was MORTIFIED. After it spilled I cleaned it all up best I could and said to my husband "I just don't want to be one of those assholes who spills popcorn and leaves it for the employees to deal with". I noticed when I said that some people sitting near me gave me a look. As we left I noticed they had spilled their popcorn everywhere, so they had obviously heard me refer to people who spill their popcorn and leave it as assholes.

Just because cleaning the theater is the employees job doesn't mean you should just leave it as a disaster zone! If you are able bodied and not wrangling a small child, if you make a mess CLEAN IT UP.