Does Saitama know whats going on around him?
Saitama does know that people around him usually treats him badly or coldly, and he really cares about it: that's why he joins the Hero Association and tries to become a hero. In the first few episodes, he cares about how people view him, but in later episodes, he just starts to ignore them( tries his best). For more information, visit the link below. 

http://onepunchman.wikia.com/wiki/Saitama