David Z I generally like ur posts but the comments that you quoted to make him look like an asshole are out of context. That cat just went into his garage and pissed in his car.
In/on distinction seems like a distinction without a difference (i.e., pissing on
the seat = pissing in
the car...). I didn't mean it like the cat pissed on his tire or something, sorry for the confusion! The only other quote I used was the one about wishing he'd killed the cat. I didn't take that out of context. Anyways aside from the cat-killing thing...
I think this sounds like a series of events that have escalated (probably unnecessary) because of poor communication. It's possible that the emails OP sent were totally benign and polite and civil. But by his own "short fuse" admission, I'm guessing "passive aggressive" is a best-case scenario. Since I don't have access to the emails, I can only make these assumptions, which may not be correct.
In any case, I stand by my previous argument: the first thing to do in these situations is to try and deal with it person to person. This might mean taking a day or two to "cool off" before you go banging down your neighbors door. If you want to follow-up with emails to establish a paper trail in case you ever have to go to court, that's fine. But the first thing you should do is talk face to face.
If the neighbor is a douchebag after
you've exhausted attempts at civil discourse, do what you have to do up to and including calling the cops/animal control/etc. but in my book you're still an asshole if you try to kill his cat.