We might identify the three social classes in the novel as "old money", "new money" and "the lower class". This is, perhaps, something of an overly-simple categorization, but it should suffice for the sake of conversation.
The "old money" group (Tom, Sloane, etc.) show a disdain for the gaudy upstart, Jay Gatsby. Gatsby is uncouth in the eyes of these people who come from money. They have not made their own fortunes but inherited them. These people, generally, do not attend Gatsby's parties.
The "new money", or noveau riche, populate Gatsby's parties. These are actresses, directors, and producers. Figures of popular culture (which is often seen as gaudy and shallow), this group is aligned with Gatsby.
The behavior of both elements of the upper class can be seen acting badly. Bickering and social drama take center stage in both circles.
The lower classes, represented by the Wilsons in the novel, are used and abused by the upper classes. When George Wilson finds that his wife is having an affair, he is unable to leave town immediately.
First he has to cajole Tom into selling him a car. The irony of this situation is indicative of the larger situation between classes. Wilson seeks to escape the evils wrought by the privileged class, but first has to gain means and permission to do so.