X-Day is the day the world will end, on July 5, 1998, which is in the future. Every year around the time of July 5th, we SubGenii organize a grand celebration of X-Day in some neo-pagan event campground out in the middle of nowhere (it used to be at Brushwood and now it's at Wisteria). The official website for 15X-Day (held in Conspiracy year 2012 at Wisteria in Pomeroy, Ohio) is on subgenius.com. BE THERE! This year it is FOR REAL! 15X-Day has a Facebook page here! If something has a Facebook page, IT MUST BE FOR REALS!!!
Anyway, X-Day is when The Rupture happens and we get to party with Alien Sex Goddesses on Pleasure Saucers while we destroy Earth with help from the X-ists, and then fly back to Planet X. As for what to do with the humans after X-Day, that's a debate between the Ivangelicals and Holocaustals. Wikipedia has plenty of biased misinformation about X-Day. Here's a video all about X-Day: