As part of the viral marketing campaign for this summer's This is the End, Seth Rogen and Co. have released a fake trailer from within the movie for a sequel to their stoner hit Pineapple Express. The plot of This is the End revolves around fictional versions of the Apatow actors shacked up together while the world is running down around them.
So it seems that while they're waiting for the apocalypse to swallow them whole, the group gets together to goof off and make fake trailers for fake sequels to their real movies. It's like the whole dream within a dream within a dream thing from Inception. Only with a lot more weed.