The worst I've ever done is put a Coles baby club pamphlet on the windscreen of a car that had no infant seat and it was a middle aged man by himself. I didn't plan it that way, I had it in my hand because I'd picked it up for myself.
Saw him walk into the shops and my friend laughed and said that I should put it on there as a joke. So I did. We giggled about it for a while and that was about it. Some people have too much time on their hands and too much angry in their system.