This is the first of Bobcat Goldthwait's directorial efforts I've seen, but I was well aware of his comedy, having once seen him in person. He was something of a bomb-thrower, basing his comedy on saying something outrageous for the sake of outrageousness and not being particular sophisticated about it. There's some of that in that World's Greatest Dad, a movie on the whole I liked, but is awfully thin gruel.
The central joke is that an obnoxious teenager, who doesn't do anything much but jerk off to Internet porn, dies accidentally by autoerotic asphyxiation. His sad sack father, a schoolteacher and frustrated writer (Robin Williams), decides to cover up the cause of his son's death and makes it look like a suicide. He then crafts a suicide note that makes his son seem like a misunderstood genius.
Goldthwait pushes this as hard as he can. Daryl Sabara does a great job making his character reprehensible, and you can believe that a parent of his would question the concept of unconditional love. Sabara is rude, crude, and without a redeeming characteristic, yet I think I've known people like him. Williams gives one of those performances that makes you forgive his work in crap like RV, playing a mild-mannered poetry teacher with gracious humanity. I particularly liked a scene where he breaks down in sobs while looking at a newsstand filled with his son's favorite porno mags.
That being said, World's Greatest Dad is a 100-minute film that could have been half that. When Williams' ruse turns his son into a deceased hero, with kids wearing his image on t-shirts and listening to his favorite music (Williams tell them it's Bruce Hornsby, who is really his favorite singer) he realizes that his life is starting to become everything he dreamed of. His secret relationship with a pretty young art teacher (Alexie Gilmore, bearing a perhaps unfortunate resemblance to Shelley Long) hits its stride, and after he fakes his son's journal, he makes contacts with publishers.
The ending is kind of predictable, and Goldthwait pulls back his claws for a resolution that is morally correct but toothless. All along I was rooting for Williams to make the most of the situation, which I guess makes me a bad person. Goldthwait does score some points satirizing the reaction to teen suicide, but I'm not sure it wasn't said already twenty years ago in Heathers ("I loved my dead gay son").