Since your neighbor has started woofing, I would suggest you contact the
city, or local government (not the police) and ask for their help. In
my town, I'm pretty sure they would look at the situation, then they
would advise your neighbor to trim his tree. If he refused, the city
would trim it and bill him.

While it is common in the US that you have the right to trim anything
that overhangs your property, there are more and more places that place
restrictions on cutting trees (usually on removing them), so I think
involvement of the local authorities would protect you.

After he trims the tree, thank him. No use in letting bad feelings fester.

By the way, its almost certain that he would not sue you for trimming
the tree. Threatening to sue is almost always just talk, and if he
actually went to a lawyer, it would end when the lawyer asked for a
retainer.

Smitty Reeves wrote:
One of my neighbors has a giant maple tree overhanging my side yard. At 72
years young, I still mow my own grass. I keep my own trees trimmed so I
don't have to do the duck & weave while mowing. I asked my neighbor if he
would mind if I trimmed his tree because of the obstacle it creates. It's
not like I'm going to be climbing on a ladder to trim this thing, but just
so it doesn't smack my glasses off. The young man let go with some four
letter words, with finishing he will sue me if I touch his tree. What
happened to the country we used to live in? Do I have to put up with this?