Some people are easily upset. You are not allowed.
This has to be a matter of prayer because you cannot afford to be a sail in the breeze of the enemy.
Genuine calm is available when there is a realization that God is sovereign over all (even flat tires) and a yielding to the reminder of the Holy Spirit.
There has to be a vision of what it is like to be solid and to resist a response that reflects the situation or the other upset person.
I grew up with father who had determined to never have harsh words. I never heard him raise his voice or say things he regretted. He was appropriately scary because wasn't a pushover.
Many have never seen someone who holds it together when there are showers of abuse or misunderstanding, false accusation or people who refuse to mind their own business.
Remember what Paul told Timothy? We are Soldiers, and we are not to be tangled in the affairs of every day life. We can't avoid them, but we do not need to be entangled by them.
You are a front line Soldier and you can't afford to be had.
Give it to Him in prayer and ask for a revelation concerning this matter.
Do it aloud. Then move on and do the next thing.