First, keep in mind that I've been a cashier at a few places and used to work in a grocery store, actually.
This cashier was around my age (20). She was friendly to the woman who was in line in front of me. They kept talking about their babies, and the woman even lingered for a moment after her groceries were bagged.
After the woman leaves, the cashier didn't smile at me or say hello. She didn't even make eye contact with me. She just starts ringing up my groceries without saying a single word.
Suddenly, she holds up one of my frozen TV dinners and asks, "You know this is the lean one, right?"
I said, "Yes, that's the one I wanted to buy."
Then she says "Oh" and tells me how she ate "the other one" (maybe she meant another brand) on her lunch break and it tasted better.
Okay, I can read and see that something has "Lean" in the brand name. I buy these because they're not that bad and are on sale often, so I usually grab a few just to have in the freezer. I really don't need her opinion on what I'm choosing to buy, and I know this sounds mean, but I really don't care that she ate some other one on her lunch break and thought it was better. Also, what about at least smiling, making eye contact and saying "Hello", instead of just starting to criticize what someone is buying?