Their intentions. Even though people may end up doing things that I find wrong, bad, mean, insulting, inappropriate, I always find it important to listen to the persons intentions, it can change the whole picture.
This is for sure not a free pass to do anything and all will be forgiven, but, at the minimum, I think its important to understand what the intention of a person is, and where they are coming from - not location wise, but what have they been through.
If someone comes up to me angry and upset and lets it out on me, most likely It wasn't me who caused that anger, so instead of retaliating and getting angry at them also, I find it much more helpful to try and understand where this person is coming from, what happened to the person and what is causing them so much anger.
Just because someone is angry at you, doesn't mean they are angry with you, they could just be letting it out and you happened to be in that place at that time.
Just because someone did something wrong in your eyes doesn't mean that that was their intention, you don't know what that person has been through..