One of two things is possible here, and they're both fairly terrifying. Possibility one is that someone has been so angered to come home and find someone parked in their spot that they've gone inside, carved up a little tribe of potatoes, put little faces on them, and then taken them downstairs to place on the hood. The second possibility is that whoever did this has a permanent potato army which they carry around in their pockets all the time, looking for an opportunity to strike.
We think that if you were faced with someone who was prepared to go this far to make a point, you'd probably just do what they wanted, and avoid parking in their space again. In fact, you'd probably just park as far away from them in the future as physically possible. None of us need to find out what the wrath of the whole potato army looks like.