It’s hard to decide which is more insufferable: the ferociously juvenile subject matter or the fact that this film, about a suicidal castaway who finds hope and a friend when a flatulent corpse washes up on the beach, has pretensions of philosophical depth to go along with the fart gags. Paul Dano stars as Hank, a beardy whiner stranded on a deserted island and about to end it all, when the long-dead “Manny” (Daniel Radcliffe) washes up. A build-up of gastric air provides propulsion and Hank is able to ride his new friend like a jetski made of rotting flesh. And that’s just the first of Manny’s surprising uses. Incredible and not in a good way.