It could be that your neighbor just has too much time on his/her hands and needs to get a life. If this is the case, I would follow what BobF said.
But, if you are parking some old junker that is rusted out and looks like h..., then I can sympathize with them. I have a neighbor that has decided to park his beat-up barge looking excuse for a boat in his driveway, right next to my lotline. He is within his rights, but it sure makes my house and the neighborhood look junky. Some people just don't exercise common sense. I assume that isn't the case with you.
Good Luck!
Dodgeman