I was put on notice and read the riot act by a cashier

I did a grocery run, and the cashier asked me if I checked the eggs. I guess I rolled my eyes and mumbled, "yes" or said it in a way she didn't like, and she opened the egg carton to make sure they were to her satisfaction. She accepted the eggs I picked out and as she was placing it in the bag, she asked, "Why the eyeroll? Why the attitude? Your generation always has an attitude." Just like that, two questions in rapid succession and then a stereotype judgment.

I don't know what generation she thought I am in, but I didn't have an attitude, I just thought it was a strange question for a cashier (who I don't know) to ask me. It actually seemed kind of an intrusive thing to ask. Anyway, I didn't know what to say, so I didn't say anything. She told me my total. I paid. And she kind of gave me a condescending smirk and moved on to the next customer in line behind me.

She made me feel like I did something wrong.