I have done the same thing. some chav parked next to me an a 306 with a **** kit on it, opened his door straight into the side of my ibiza i had at the time, placing a little dent in the door. right in the middle on the style line. so i got out, when hed gone, got a plastic bag from the boot along with a latex glove (carry em incase need to change wheel), and much to the amusement of my mate who was sat in the back, i found a pile of dog ****, got some on the bag and then smeared it under both his door handles and drove off. He wouldnt be able to tell id done anything till he opened the door.
This was miles away from where i live, im a bit parra about doing things like that close to home.
Fool.