A serious problem...

[golfer]

yeah i agree with the others if you know him you may want to talk to him, or his family and make sure he is ok... if that doesn't go well you can probably put in an anonymous wellness check call to the cops... but i would try other options first as he is your neighbor and you do have to live next to him...

[JoeyB]

Any updates, JoeyB?

Serious answer.

Sounds as if the guy has been there for awhile (for JoeyB to somewhat know his habits and mannerisms)
I would take some time to approach him personally, try to find out what is going on, and basically let him rant for awhile in order to do so. If at that point I felt he was danger to himself or others, I would call the Cops, if not I would try to explain that he is upsetting the neighbors by his actions, and keep an eye on him.
I have a neighbor that is mentally handicapped. I didn't know it until I talked with a former co-worker. Turns out the neighbors is the co-workers uncle. He's basically harmless, but does tend to "fort" up in the abandoned acre beside my property. He's out there at night at times hollering and yelling. I've talked with him over the years I've lived here, and though he sometimes makes my wife nervous, he is pretty much harmless, and is well aware that my property is off limits.

yeah i agree with the others if you know him you may want to talk to him, or his family and make sure he is ok... if that doesn't go well you can probably put in an anonymous wellness check call to the cops... but i would try other options first as he is your neighbor and you do have to live next to him...

I've come to the conclusion he may have some mental illness, but specifically seems to be playing out an argument scenario.

For three days he did the ranting and pacing, on the fourth day he added colorful arm movements, including one that I've optimistically decided is a tribute to the famous Atlanta Braves 'chop'. The next day, I was getting ready to walk my dog when I saw him twenty feet away in his side yard, pointing and yelling at someone. Except...he was alone.

But as I said, I really think all of it was him acting out an argument or discussion he'd like to have with that mildly retarded guy who lives there. Meanwhile, I keep waving hello to him when I'm outside and he comes out the door, and he waves back. Lately he's a bit calmed down and paces less, though he hasn't stopped. And he even walked up to and talked to me briefly today and was very lucid.

I'm keeping things pleasant and low key.