If you get along with your hippie-redneck neighbor, why don't you just ask him? Maybe he just has a little handicap.
Some people have a little disability so that they can hardly smell or even cannot smell at all. I have this problem, it was caused by an accident when I was 2 years old. I am very grateful when people tell me that my flat or I have funny smells as I cannot smell it myself, and I encourage people to tell me these things. It's really a sort of handicap as even if you are careful, you might miss out something smelly and you cannot know everything by heart about which things may smell and which not, and if the smell is lovely or awful, decent or strong. Even if you try your best and take good care, your flat might still end up stinking if you have this disability, or your shampoo might stink and you don't know it.
I probably wouldn't have smelled the rotting rat in the wall of my office, for example (this occurred before I worked there). I cannot smell the typical public toilet smells, and I cannot smell any flowers or farts. Exhaust emissions smell like a campfire for me but I can hardly smell them. I can hardly smell even the most extreme kinds of cheese, and if I can, they smell decent and lovely to me (Roquefort, Limburger, Esrom, goat cheese etc.). Burning rubber has a very decent musky smell which I like a lot and even turns me on, and terpentine smells good, lovely and fresh like a lemon plantage at the sea-shore. Both are my favourite odors, but I know they are bad for my health so I keep away from them. Perfume I either cannot smell at all or it has a putrid or chemical smell for me which really makes my stomach turn. You get the picture...
Maybe that's your neighbor's problem and he is not aware of the smell in his flat or thinks it smells lovely and decent. Many people don't tell this handicap to everyone to avoid questioning, pity or non-belief, and it is also a bit shameful to admit you might stink without knowing it.