Never had a customer get upset with me however over the course of years you always get that one employee that thinks they know it all and because they're having a bad day they choose to make the happy employees feel like them ( it's like when someone yawns walking by you and then you yawn ) misery likes keeping company etc etc this is how you avoid this problem always remember it's there Zoo and their animals keep on smiling and walk away. they'll find someone else that will engage in their anger. and it won't affect you at all.