I would NOT stoop to his level and do the stupid junk that he does. I do agree that you don't want your neighbor pissed at you. BUT... This is what I would do. I would call the local law enforcement. (Not for him talking about you, but for putting crap on your sidewalk and for threatening you) You can really make his life hell. If you need advice on what you should do on the law enforcement side, send me a PM.