I went to the supermarket, and I was at the Customer Service desk signing up for a store card so I could save money (don't you hate that you need a card to get the sales?). An old woman came up while I was there because she had forgotten her purse, and a middle aged woman helped her and was very nice to her face. When the old lady was out of earshot, she said to the girl who was helping me "Oh, that was the IDIOT who left her purse".
To me, that is the height of unprofessionalism. You don't call a customer an idiot in front of another customer, even if they do something really stupid like leave their purse at a store. Shit happens, it was an OLD LADY. Save your snarky comments for your coffee break in the employee lounge.
I'm probably going to call the store manager to complain, but I doubt it would make much of a difference.