diversity. and neighbors

The neighbor who shares a wall with us is a Japenese American with long hair an a goatee. He has a very loud voice and tends to rant frequently. He yells at his girlfriend (who is also our neighbor) and throws things against our shared wall. He has a sticker on his SUV that reads 'next door neighbors: singing, dancing and cutting people' He has never cut me, or anyone else as far as I have been aware. Every time I have encountered him he has been friendly and once told Marissa and I that we are awesome neighbors.
A handful of times I have locked my door during one of his berzerker phases because I thought it was possible he might come into my apartment. Once he and some friends were up late being loud and listening to music while Marissa and I were trying to sleep so I knocked 3 times on the wall and I heard him say to his friends that he didn't care if we were upset and that if necessary he would come over to our apartment and beat us up. I have several times heard him threaten to beat people up. One person he apparently owes money to, but doesn't mind because he 'is tough' and can take up to 'three of them'.
His girlfriend is very quiet and I almost never hear her speak. One of the few times I heard her she was talking about getting a gym membership, which caused him to go on a rant about how it was a bad idea because she would maybe go once or twice then never again.
Whenever I hear him I feel better about myself because whatever faults I have I am much kinder than he is. And my voice is not nearly as loud. And I don't watch 10 episodes of M*A*S*H each day. And I do things besides watch M*A*S*H, yell or play video games.
The wall we share is very thin in terms of sound. Sometimes I can hear farts or burps. We often keep the fan on our stove on to block out the sound. Recently I have noticed that it seems they having begun keeping their hood fan on. They also keep their downstairs windows blocked out from light for some reason. The layout of our apartments are mirror images of each other, so I am intimately familiar of the layout of their apartment. I know that their downstairs is naturally very dark because ours is. I try and let as much light in as I can downstairs. In the winter time the sun sets here around 4:30 so sunlight feels like a precious commodity. That they would want to make their living room even darker than it already is, is something I find unusual and unrelatable. I sometimes wonder what our neighbors think of us. Whenever I have written about our nieghbor online a part of me worries that he is somehow aware of it. I'm not sure he even knows my name though.
One time he was talking to a friend loudly and Marissa and I paused whatever we were doing to listen and I then heard our neighbor whisper to his friend "I think our neighbors are listening"