Why does my neighbor's son do this to himself?

I'm not understanding this maybe I don't need to, but my neighbor's son who is 19 years old has horrible hygiene upkeep. In fact he makes it known he will wear the same pair of socks for weeks until you seem them turn black and smell bad. The same with clothes. He will wear the same pairs of clothes until dirty and smell for weeks along with that not ever shower. He's gone an entire month without showering before. He will end up smelling so bad to the point you have to get away by making an excuse to not talk to the neighbors. His odor is that offensive. Yet, he will complain all the time why he smells so bad and has athletes foot and says he's too lazy to shower etc. How can someone be that lazy for his hygiene to get that bad? My point in all of this is because my neighbors keep asking me why I do not talk to them anymore. It's not the mother's fault, but I just can't be around there anymore with how bad her son stinks. What kind of excuse can I say politely as to why I do not associate myself there anymore?