Why Did I Do That?

So I have this weird habit of stealing my little sister's favorite snacks when she’s out. It's not like I'm hungry or anything; it just seems funny to take her stuff and watch the drama unfold when she gets back. But then, every time, seeing how upset she is makes me feel guilty. And I always regret it afterward. Why can't I resist this little thrill of making someone else’s day bad for no real reason? It's not like we don’t have enough snacks in the house.