One who despises persons of lower social position

One word substitute is Snob.

Prim: feeling or showing disapproval of anything regarded as improper; stiffly correct.
Snob: a person with an exaggerated respect for high social position or wealth who seeks to associate with social superiors and looks down on those regarded as socially inferior.
Prig: a self-righteously moralistic person who behaves as if they are superior to others.
Aristocrat: a member of the aristocracy.