Hey there RHU, it's Trivia Grrl back with a short one from many years ago.
I was working in a toy shop at the time. A customer stopped me to ask about some Lego, and as we were chatting I noticed that her toddler son had a packet of crisps. (Chips if you're in the USA.) Nothing out of the ordinary there, lots of parents shut their kids up with food while they're shopping. But this boy is carefully, thoughtfully, dropping one crisp at a time on the floor, and grinding them into dust with his foot. The dust's getting caught in the carpet and I'm already anticipating a lot of trouble trying to vacuum it up later.
Me: "Oh, hey, please don't do that, pet!" (big smile so it doesn't seem like I'm angry)
So far, the mother has been brisk but not actually rude. Now, however, I seem to have flipped a switch.
Mother: "Don't tell my son what to do! I'm his mother, it's my place to tell him what to do!"
Me: (in my head) "Then please start telling him what to do..."
Me: (out loud) "My apologies, it's just that he's making a mess there."
Mother: "So? He can do that if he wants! Thank you for your help, I'll look at them on my own now."
Translation: Fuck you, he's not messing up my house so I don't care.
Since there was nothing else I could do, I left them there, but I did get the vacuum and leave it nearby. She stayed there for another ten minutes, and when I went to check after they'd left I found that not only was the floor covered in crumbs, one or another of them had mashed crumbs all over the shelves and boxes as well...