Ticket punchers are the ones who have it come back at them, chief. The tree sitter isn't hurting anybody. You're the one who imagined causing him/her an injury, AND you imagined yourself taking pleasure in it. 

In some theist traditions, a thought like that is itself a pretty bad sin. 

I'm sending waves of loving-kindness at you, bro'. Maybe that will be enough. Maybe not. Maybe you should send some L-K at the tree sitter. How about it?