I once had a lady with kids. The woman turned to her kids as I was ringing up her groceries and said to them "this is what happens when you don't go to college. Do you want to bag groceries all your life?" I finished her order, handed her receipt and told her calmly. "Mam' I have a college degree, and have been a cashier for over 20 years. Have a nice day."
I have had bad tellers and good tellers. If they are a bit snippy, I chalk it up to a bad day. If they are down right rude, well, there are always other tellers I can go to instead of that particular one. And I would tell them, I do not want to be waited on by the rude teller anymore and leave it at that. It's like having a waiter at a resturant. Reward polite service and bad service show them the monetary value of your size 9 boot tip.
Hugs and Smiles,
Garoulady