Eggs, eggs, eggs, eggs...

The two islands of fictional New York, the east and west eggs, are polarized in cultures.
East egg, where Tom originates, is full of stuffed-shirts who simply inherit the money of their ancestors over several generations. This money as somewhat of a code of honor, and many people from east egg keep themselves in good posture, don't act out, and do their very best to avoid situations that would stir gossipers. However, this also makes them really snooty, and very bland.
However, the people of west egg are all about the life of glamor and having fun. The money they have is recently obtained, and as the old saying goes, "Easy come, easy go." People like Gatsby and Jordan throw away their money willy-nilly without a second thought to have people run amok and make utter fools of themselves.