I remember while working for a small retail store, I was asked to do a shift in a store the next town over. The shift went well until this one couple entered the store.
Good God, their 5 year old daughter was just screaming for toys/candy like she would die of cancer if she didn't get them. Finally, the mother managed to satiate the brat by getting her a doll. The father left the store as the daughter and mother lined up.
I, at this point, was unbothered by the noise (used to live with 5 year old twins). It was when I was down to the last item I needed to scan that the shit hit the fan: the doll that was in the daughter's hand.
I politely asked the kid, "Hey, I need that for a minute. Mind if I see it, please? I promise to give it back."
The mother looks straight up at me and says with the bitchiest tone I've heard IRL, "She'll give it to you when I tell her to, you stupid BITCH!"
After that, the mother snatched the toy and threw it on the counter. I rang it up, and handed it back, and finished up the mother's transaction.
As she left, I said in the sweetest, most polite tone I could muster, "I hope you have a wonderful day, ma'am," and smiled.
The only good thing I ever learned from my ex-mother: kill 'em with kindness. The look on the customer's face as she exited the store was well worth the trouble and the long line after her.