Uncalled for

I don't understand people sometimes. Why do they have to be so mean? It makes not a lick of sense to me.
Like a few days ago when this unnamed person was messing with my cousin. He started to make fun of her being in a wheelchair. And being that she is close family and I love her to death, I wasn't having that crap. Not to mention making fun of things that people can't help is way over the line. It eventually came down to me coming to the conclusion that he wasn't worth my time. I eventually told him that if he didn't leave her alone that he would have more than just me to deal with.
For a few hours after that I was shaking with anger. But after thinking on it a bit I realized that I had made someone happy. My cousin was happy that I would be there for her no matter what the problem was. And that was all that should have mattered.