I remember reading a story or listening to a story where someone was treated badly by another, but he did not take offense, as this person saw the suffering in the other person that caused this action upon himself. He knew that anyone who criticized him for something, they were, in essence, criticizing themselves. As within, so without. If you are mad about someone being late, perhaps you are late in some part of your life. The only reason you take offense to something someone else does is because you see a part of yourself that has this same sort of problem. So I can definitely see how working on yourself to improve in this area would help.
It is all in how you define the problem. In one of Steve's earlier articles or podcasts, he gives an example that someone's roommate is stressing this person out. Instead of working on stopping the roommate from stressing you out, the approach he took was working on your own stress, and the roommate will improve dramatically. It was something along these lines and it rings true, at least in my experience.