Sounds like relations between these two neighbors is already pretty bad -- the guy crosses the street to walk on the other side? Because he was asked not to point his security camera at someone else's property? Some people are just... children.

Wait til you see two neighbors arguing about property lines.

At least that I can understand. It has implications on right of way, usage, easements, property values, etc. without even getting into issues of adverse possession (which combined with property value issues can become real trouble).

The line between "please don't point your camera onto my property" - something I would respect as a courtesy regardless of the law - and "I'm going to cross the street not to interact with this person" goes straight through mental illness in my opinion. Normal, stable people do not behave that way.

A lot of "Normal" people are not stable. People are petty, vindictive and childish, to think anything else is just flying in the face of evidence.