Anyone who uses the reputation of an organization they belong to in order to try to further their career/social advancement, and use it as a pedestal to look down on others who aren't a member of said organization. Instead of carrying the values of the organization, they attempt to let the values of the organization carry them, usually to their detriment.
Tom is a card-carrying member of his fraternity. He feels that wearing his letters gives him an excuse to be an asshole to everyone who's not one of his brothers, and assumes that his connections will get him a job after college, even though he drinks and jacks off all day and never goes to class.
Susan is a card-carrying member of PETA. Her entire identity is built around the ideals of one organization. She is not imaginative enough to develop a personality of her own, so instead she adopts the angry bleeding-heart liberal stereotype.