I know you've just added this question but I was just about to go when I saw this post and thought I'll answer it. :)
Ahhh, this is a great question and one that every single person lives several times and sometimes on daily, weekly basis.
They call it personality. Your personality determines your actions. It also depends on life experiences, the state of your mood, the health, the wheather and several more factors.
But the biggest overall factor that would influence you would be your personality and your character strength.
You need to vent it off, that is what I do. I would take a deep breath, hold on to it for several seconds to get my positive energy up and then think deeply, so quickly of the situation.
In most things in life you would want to let it go if it's not life threatening. If it's an argument with someone you know then you would definitely be wise to let it go. There is a lesson involved in every corner of our lifes and these occassions are one of those lessons. It is a test of your personality and the strength of your character.
Lifes not worth it trying to get mad or even. It takes a big personality to let it go in addition with forgiving and understanding.