The X-Card is an optional tool that allows anyone in your game (including you) to edit out any content anyone is uncomfortable with as you play.
Since most RPGs are improvisational and we won't know what will happen till it happens, it's possible the game will go in a direction people don't want. An X-Card is a simple tool to fix problems as they arise.
The X-Card is published under a Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) License. Simply credit John Stavropoulos and link to this document here: http://tinyurl.com/x-card-rpg