The person who seems angry may have low blood sugar, may have gotten a terrible night’s sleep, or could be severely dehydrated. Their unprovoked anger has a root cause, even if the cause is unavailable to you. A person’s physical state can produce a poor, un-resourceful mental state.
An unusually upset person who speaks to you in a way you feel is inappropriate for the circumstances may be struggling in their role, struggling in their personal life, or under immense pressure due to some external circumstances. The pressure they feel may manifest itself when that stimulus is not present.
When a person’s actions are out of line with what would be considered polite and professional, there is invariably something driving that behavior. They may be struggling to meet some deep human need, like psychological safety, or they may fear some potential harm they believe may befall them. The fact that you see only the symptoms and not what is causing them does not mean there is not a cause.
None of these things may have anything whatsoever to do with you. It can feel as if you are being treated unfairly, and perhaps it is true. Even if it isn’t easy, and even if it doesn’t seem fair, you can decide to recognize that human beings tend to be short with others when they are under what they perceive to be immense pressure or are racked with fear. You can choose to exercise your compassion by recognizing there is a cause or forgive them for whatever offense you may have felt.
When the offense has nothing to do with you, there is no reason for you to perceive it as such, as you were not the cause. You don’t need to allow someone else’s state to change yours.