When used in gaming it is used to describe someone who looks down on those who are a lower rank or level than they are.
Player 1: Leave this lobby now!
Player 2: Why?
Player 1: because you are a level 2.
Player 2: Shut up you stupid rankist.
Player 2: Why?
Player 1: because you are a level 2.
Player 2: Shut up you stupid rankist.
by Chiotis December 12, 2013