One memory coming up...
Years ago, when I was nine, I punched a kid on the school bus. Don't judge me too harshly; he deserved it. If I remember correctly, he spent the entire bus ride picking on me. There's only so much a kid can take, right? So I hit him. And it worked... he fell back.
But then he did the worst possible thing in response, as hindsight would show. He didn't tell on me...and he didn't fight back. Instead, he covered his bloody nose, and paid me a compliment with a trembling voice: "You're a really good fighter."
It made me sick at the time, and I feel sick right now, as I write about it. </memory>