NASA has already spent some time explaining why all the 2012 End of the World theories are as stupid as those who postulate them. This video is not by NASA, but it summarises things perfectly.
Of course, the doomsday imbeciles will not care about reality the same way rapture imbeciles didn’t care either. But hey, if at least one of them realises their stupidity after watching it, it would be worth it. [Thanks Karl!]