Based on recent experience, I need to add a new rule to my Life Rules list.
Default to kindness.
Chances are, you're tired, or annoyed, or frustrated, or really wanting to be somewhere else. All of that happens, don't take it out on the next person.
You don't need to be an ass. You don't need to be short. You don't need to be mean or "objective" or righteous or distracted.
Take a deep breath. Smile, if only for yourself. Reset the moment.
And be kind.