My grandmother had gone to the grocery store to pick up a few things, and didn't have a problem until she was ready to pay at the checkout. She was paying with her debit card, and either she was having issues with the card machine reading her card, or was being too slow by the cashier's standards, because after a moment, the cashier literally snatched the card out of her hand, turned the card machine around, and slid it through.
Now, I'll be the first to admit my grandmother isn't exactly the speediest of people. And being a grocery cashier myself, I've sometimes had customers who have repeated "card read errors" from sliding their cards too fast/slow, or who have some sort of disability preventing them from sliding their card or something, and if they happen to have repeated trouble, I'll ask if they'd like me to try and slide it, so long as they're okay with it. Oftentimes, they'll happily agree, other times, they'll decline, whatever, I move on with my life.
But in what universe is is acceptable to outright grab someone's debit/credit card out of their hand, without so much as asking if it's alright, and run it yourself? Unfortunately, my grandmother didn't do anything about it, as far as I know, though I really wish she had. I wish I'd been there, because I most definitely would have asked to speak to a supervisor about that. I'm sorry, but that's unacceptable.