Ok, so the joke is that everyone in Seinfeld are horrible people. But like you see George Constanza and Neuman carry a lot of the let me just say negative traits. George and Jerry are kind of the main characters while Neuman is almost like a foil. They are all scheming but like.
This is a real tall order to explain, Seinfeld was on for so long. And I could say that George is narcissistic, petty, vindictive. But that applies to ALL of them. I'll just say that Neuman and George are like, the top of the pile of that metric.