The American Association of Retired Persons (AARP) appeared in the Season Seven episode, "Grey Dawn". The group is a non-profit organization that lobbies the United States government on behalf of elderly and retired citizens.
Background
The townsfolk of South Park vote to have the drivers licenses of the elderly revoked, due to the many accidents they cause. In response to this, Marvin Marsh leads the other tenants of the Shady Acres retirement home in a militant protest.
The AARP soon later captures the town, holds the citizens hostage, and makes unfair demands in their favor. Before their threats are allowed to be carried out, the elderly are defeated when their food supply is cut off at the Country Kitchen Buffet.