Sorry if your question has been answered better further up but i’m not reading all the replies.
We had a problem with our elderly neighbour a few years back, she hated us with a passion as did her relatives, a few arguments over hedge clippings every once in a while.
But her TV drove us insane she had it sooooooo loud you could here everthing she watched put up with it for 5 years or so, but when the little uns arrived we were having none of it. Spoke to her and relatives about it but they didn’t want to know told us it was our problem.
Got onto to Council Enviroment Officer, Council sorted it within 2 weeks, as you don’t get on with anyway you’ve nothing to loose and it would save you the expense of soundproofing.
You really don’t want to be taking it to a violent level unless obviously he starts it.
Good Luck