When my children were small — say 4 and 2 years old — we used to go to a video store regularly (this was…a couple of years ago). The guy who worked there was usually quite affable and chatted with me and the kids, etc. One day, though, something had happened — it was raining, and my kids were restless, and he was glaring and snarling — like a completely different person. When I went to check out, he snapped at me over something, and I looked him in the eye and said “Look, I’m sorry you’re having a bad day.” I did NOT say it in a particularly sympathetic tone. Nevertheless, he simmered down and was at least nominally polite for the remainder of our interaction.

Never went back, though.