you know, i was kind of in a similar situation a while ago.
As many of you know, i still live at home with my parents. Unfortunately our driveway is not flat, and its kind of at an angle. So, other normal driveways in our neighborhood fit 4 cars, but ours only fit 2. So, i always park my car along the curb in front of the house.
Well our neighbors constantly have people over at their house. So, one day their "friends" decide to park where i ALWAYS park, and since they are always going to their house, they KNOW that! So anyways, i had to park elsewhere, which was a pain because we dont have room to park along the curb on the other side since it blocks my other neighbor's driveway. This started happening more and more frequently. So one morning before my dad leaves for work he writes this "note" letting them know that i always park my car where their friends have been parking, and since its really the only parking spot that we have besides the driveway, he would appreciate it if they parked on their part of the curb in front of THEIR house!
It was so embarassing, but they got the point because they never park there, ever! You'd think we are like enemies or something but my family and theirs are very close.... we even invited them to our new year's bash, which they came to and had a blast!