According to the Mayan calendar, the world is supposed to end on Dec. 21. If that happens, audiences won't get to see " This Is The End ," which is too bad since it looks really, really funny. Watch the very R-rated " This Is The End " trailer below, with a special introduction from Rogen and Franco . Some backstory: Previously called " Jay & Seth Vs. The Apocalypse " and " The End of the World ," " This Is The End " started as a short film starring Seth Rogen and Jay Baruchel as versions of themselves dealing with the end of time. " This Is The End " expands on that premise, making Rogen, Baruchel, Jonah Hill, Craig Robinson, James Franco and Danny McBride survivors of the apocalypse, which strikes during a Hollywood party at Franco's place. (Sorry, Michael Cera and Jason Segel , both mentioned as fatalities in the clip.) More deaths likely follow, and judging from the very R-rated trailer above, they wi