Why do wealthy people and intelligent people become so arrogant and rude?

I always said if I ever become one or both I would always be nice to people because I know what it feels like to be stepped on and looked down upon. To be honest these people are not treated badly by others as much as the average person is, because people respect them, yet they always seem to be in a bad mood as if they are mad with the world that gives them their privileges. I'm asking because i have this roommate who is really good at physics and he always belittles other people suggestion and their knowledge about it in a rather condescending way like for eg. if I dont know a famous physicist or say coulomb when I meant Joule he says " You obviously don't any physics" then he starts ignoring me , as if he was born bright and wasnt a stupid babbling baby at one point in his life. Plus i know there are other subject areas where he can't even put two sentences together without sounding stupid so whats with the arrogance?