Work retail during the holidays and you’ll see every kind of person in one afternoon. Most of them are just tired.

Six hours behind a counter in December is an education in people. The ones who snap are mostly not cruel; they have been in four shops, they are behind on money, somebody at home is ill, and you happened to be standing there when it tipped over. A rude stranger is usually a tired stranger with no interest in you at all.

Try making tiredness your first guess for a week. It changes what you say back, and it keeps the shift from costing you your mood. Then extend it to the people who are not customers, including whoever snapped at you at home last night.