I had a neighbor who was from India and when her MIL would visit the MIL would wipe any crumbs on the table onto the floor. This is in my neighbor’s home. Her MIL was from a fairly wealthy family, labor is cheap in India, so at home when crumbs fell to the floor the servants were there to sweep 3 times a day. But here, in the US, my neighbor would up having to sweep it up, and her MIL never got a clue, never gave a shit, just kept doing what she was accustomed to. But, that is a cultural difference, while I am pretty sure here in America the people most like to trash a place are the very people who would never have servants in their own home. In fact, I would go as far to say the very wealthy would be much less likely to leave a mess in a dressing room or leave a mess behind in general. Stereotyping, but that has been my experience.
I think it is good to say smething, because even if the parent doesn’t care what you said, there is a chance the child learns it is not acceptable. My MIL akways says it is good for children to be exposed to many adults, learn different opinions and thoughts, and I think that is very wise. It also makes me think of a Q regarding cigerette butts. Augustlan pointed out as a kid she never thought of them as litter, her mom dumped out the butss and put them out on the ground. Then later she realized it was not different than any other type of litter. So, I think calling this sort of thing to people’s attention can possibly give them an aha moment. It might only be 1 in 20 times you say something. But the one time is worth it in my opinion.
It doesn’t always have to be that you accuse the person of being awful, one can just point out they left their trash behind, or offer to help pick up an accidental spill.