Not with customers but with the reminder that it is like living in a student house. Sink perpetually full of cold water with a teaspoon or two at the bottom. Coffee spills on the workstop. Half eaten packets of food that seem to spread. All little things that don't really matter but still irritate.
A friend of mine posted a picture on Facebook recently that said
"Breathe in Peace
Breathe out Love"
Normally I take those sort of phrases with a pinch of salt, but that one seemed to stick in my head. Reminding myself of it helped me get through a few moments over Christmas when I was worrying about things, feeling stressed or thinking uncharitable thoughts about people!
Try it next time you are feeling wound up, and combine it with a deep breath in and a deep breath out, it works for me...