This year my husband (who teaches high school chemistry) has a blind student. He's told me a lot about her and I met her once while in DH's classroom (remember, we teach at the same high school).
She told me she has heard my voice before and I told her I'd say hi next time she walked by my classroom.
Yesterday I saw her while I was holding the door open for some of my students. I said "hi!" and she said hi and then asked me how my day was. I said great, and she said her day was going well. I said "That's great! See you later!".
Then I put my palm to my forehead and realized how inappropriate my comment was.