One of the most effective techniques I learned years ago in a workplace leadership training course is called active listening. It takes practice, but it results in you "winning" and the other person thinking "what just happened here". Google
LET active listening. or go to
http://www.gordontraining.com/free-workplace-articles/active-listening/.
Here's how it would work:
Neighbor: "your gonna wash the paint off that thing"
You: you say washing my car is going to damage the paint?
N: you do it so much that you will wreck the paint
Y: Washing my car with correct soap, towels, and water will wreck it?
N: But you do it so often.
Y: Your saying I wash my car too much?
N: Yes. There's barely a spec of dirt on it and that's way too much work.
Y: So, you are saying that my hobby and relaxation of washing my car is work?
N: Yes. I hate washing cars because it is so much work.
Y: So, because you hate washing cars, I should too?
N: Err, umm, no, that's not what I am saying.
Y: So, as long as I am enjoying myself washing my car....that's o.k. with you???
N: Err, umm.....yea, I am just teasing you a bit.
He should now leave you alone. I have crushed power hungry bosses with this technique and they go away flustered, wondering what happened (no argument). It helps to understand the whole methodology, but in this case you don't take ownership of the neighbors problem and you turn it back onto him and coerce him to solve his own problem.