I'm pretty sure that person should be hunted down and killed immediately. No need to have worthless people like that roaming around.
And yes, there is ALWAYS a reason people do stupid shit like this. Unfortunately they are normally stupid reasons like, jealously. There was a story of a guy getting his H2 Hummer keyed because of some tree hugger didn't approve of his gas guzzling vehicle. Fortunately he had a camera mounted on his truck and got a PERFECT video of him keying his car. He later turned over the video to the authorities where they quickly apprehended him. However it would have been better if he kept it to himself and went on a little man hunt.