I play Minecraft with my 9 yr old nephew and he's a mostly
   gentle soul with a really wicked cruel streak I try to point out
   to him.

   One day, we had some NPCs - they had names on their heads and
   their professions. Not feeling in a peaceful mood, he rounded
   them up to drop them in lava via a trap door in a cage.

   So I walked around the cage and said, "Chris the Baker, you must
   pay for your crimes...." and the like.

   In the chat, nephew writes, "Oh, they didn't do anything wrong."

   All I had to type back is: "Oh. "

   Well, within a few minutes, he had modified the roleplay so that
   he was the evil Wizard and I was to break them out when he had
   his back turned.

   *Much* better scenerio. I do what I can. I suspect he'll always
   have a slight "revenge" streak in him, but if he's at least
   aware of social implications [or just pretends around me], I'm
   ok with that.