Once, I took pleasure in hurting someone.
I was a white belt at a Brazilian Jiu-Jitsu gym, and my knee was hurting toward the end of the class, so I asked my sparring partner — another white belt, who was there for like two weeks — if we could take it easy. He said yes.
I went at 25% effort, and off the bat the dude went anywhere from 80-100%. To boot, he attempts a heelhook.
That's one of the most dangerous moves, one that should never be attempted by beginners. It can cripple someone for life. To make things worse, this guy didn't know what he was doing.
I tapped to avoid the risk of becoming permanently crippled.
We reset, I got on top of him and I leaned my fists into his kidneys; while punches aren't allowed, putting pressure on someone's stomach is. Using maximum effort, I did this with as much bodyweight as possible, driving with my feet. It felt great. Fuck that guy.