There is a moment between the reception of input, and the ‘resultant’ chosen output. That upon the context of a frustrating customer, or rather upset friend, our decision to how we respond is just that: our decision. The difference between people and people when cooler heads prevail, is simply that the time between input and output is larger. The longer one has to decide upon something up to a point, the better their answer or output may be. Just like more immediate triggers, one can forge new triggers that are of the positive sentiment. To automatically respond with jarring kindness when one raises their voice to disrespect and so on.
Meditate.