Imagine a sensitive but savagely satirical comedy, written and directed by Bobcat Goldthwait, about the perils of both autoerotic asphyxiation and literary duplicity, in which a rueful Robin Williams gets to say, “I loved him. He was my son. He was also a douchebag.” Sounds promising, right? Williams’ sullen single father, a fame-craving unpublished novelist and teacher of poetry to uninterested high schoolers, is indeed just about the opposite of his righteous sage from Dead Poets Society, and all the more refreshing for it. Daryl Sabara, as his truly hateful teenaged spawn, is fearless. Goldthwait’s scenario is slight, and his elaboration uneven, but the movie scores with its scrappy attack on the sentimental hypocrisy of our selfishly selective memories. Part of what World’s Greatest Dad gets very right is the sadly, sickly funny desperation that adolescence and middle age so often have in common.