Hi, Lisa. I really appreciate you taking the time to read and share your story and experience here.
I think such confrontational moments like that can be very crucial in our lives. In regard to your story, gender pronouns might be something "unusual" for cisgender people, but it might mean a lot to "them". So regardless of our intentions, I think if we at least realize what or how much it means to them, we can treat others better and cultivate a healthier tolerance among us. I'm glad you had that conversation with the cashier. :)
Again, thank you for sharing your story, Lisa. Reading personal stories like this can help others understand the topic deeper on a personal level :)