Talk to them - there might be a reason. We have ample off street parking at our place, but there are two idiots that have moved into our streets with noisy cars that they drive like hoons around our previously quiet neighbourhood, and then park outside our DD's bedroom. So I have taken to parking in that spot so that they can't. I got a note on my windscreen, which was really rudely worded, but I just don't give a toss, when they both also have OSP and are just too lazy to open their gates and use it.