How can beggars and bums withstand stuff that would most probably destroy you, such as eating rotten stuff from the trash, drinking like there's no tomorrow, mass of maggots on the leg, never shower, etc?

I have a good answer for this! My grandma was a germaphobe so she cleaned everything so thoroughly that my dad got sick as a baby from something kids normally don't get sick from due to-frequent exposure to germs from putting stuff in their mouths. Because my dad did not have that frequent exposure because everything he put in his mouth was too clean. Same goes for visiting a country with lower quality drinking water than you are used too. It gives you problems while the locals dgaf. Its all about what you are used too