Is it normal that i want to kill bullies?

Before you freak out on me, hear me out.

I have a brother. We go to the same college, hell, we're even roommates. He's not popular at all, but I'm the second most popular guy at school. The problem is: every single time he gets back to the dorm room, he comes back being the victim of a swirly or being hung in the closet by his underwear. Every single time, I get mad! I get so mad, that just thinking about it makes me want to kill the people who did that to him. Not just quick deaths either, I actually start planning out fantasies where they're begging for death by the end.

I got into a fight with one of these guys that did that to him once (the bullying, not the killing), and when I was fighting him, I was happy. Not just kid on Christmas happy, I was ecstatic. I was the happiest I had ever been in my life. Is this normal, or should I see a psychiatrist?