Neighbors parking in front of MY house...Irritating!!

I usually don't complain to much about the little things. But its just getting on my very last nerve lately. Our neighbors on one side of us haven't even lived there 2-3 months and this is the umpteenth time that they have parked in front of MY house!!!! They have a driveway and in front of their own house they could park at and they have a carport to park a vehicle in/under but do they do that??? Nope they would rather park in front of my house and this time they parked to where the mail man can't even get to the darn mailbox!!! How irritating and its not like were in apartments or something, were in houses and they have 3 freaking vehicles and they can't figure out how to park 1 in the carport, 1 in the driveway and the other one in front of their Own house!!! Nope they park in front of mine!!! One of their friends one day had asked me while I was outside if they could park in front but it was closer to their driveway then my mailbox and because he asked I said that's fine but dammit I am about to blow my lid on them for parking in front of my house by my looks like its my vehicle and it looks like I am the idiot parking in the street and not giving the mailman room to deliver..ugh!!!!
I've went over there and knocked on the answer so I am leaving it alone for now but I swear if they freaking move the truck out of the front of my house I think that I am going to go and park my van in front of my house but close to their driveway and see if they get the hint!!! Geez!