Grade: C+

Talk about a one-joke movie. “The Aristocrats” is a documentary about a scabrous, scatological gag that’s been passed down through generations of stand-up comics–not in terms of being used in their acts, but rather being batted about as a behind-the-scenes professional secret, a sort of cultish verbal handshake through which the members of the fraternity can exhibit their own peculiar gifts. Basically the joke is no more than a simple set-up and standard punch line, to which each comic adds a middle section as long and as disgusting as he can contrive. One shows his facility by the amount and degree of repulsive detail that he comes up with. The basic joke that begins with a guy walking into an agent’s office to describe his family’s act and ends with the revelation that it’s called “The Aristocrats” is really a kind of comedic theme, and what this picture does is provide plenty of variations on it in the form of middle sections describing the act in the grossest possible terms, told by scores of its most eminent practitioners. But it also offers amusing excursus on the joke’s history and observations on what it represents for the stand-up community.

Of course, this isn’t the first time that bawdy–some would say smutty–humor has been the subject of scrutiny. At one point a interviewee holds up a copy of the notorious book on dirty jokes by the famous bibliographer of erotica and pornography Gershon Legman, who, until his death in 1999, catalogued and recorded just about every variety of such stuff imaginable. But Legman tried to present the material in an ostensibly scholarly way, although he was always inclined to subjective outbursts that showed his personal dislikes. Here the approach of Paul Provenza and his co-executive producer Penn Jillette, who also appears with his mute partner-in-magic Teller, is more light-hearted and anecdotal. So many well-known comics appear that it’s hard to pick out all the high spots, but George Carlin is especially articulate, and some of the best moments are provided by lesser lights like Martin Mull, Chuck McCann, Rick Overton and Larry Storch, along with unlikely practitioners of nasty language like Bob Saget. On the other hand, any movie that leads up to a flamboyant version of the joke by Gilbert Gottfried–with his raspy voice, his tendency to shout and his squinty eyes easily one of the irritating of all comedians–has something of a structural problem.

The fact is that Gottfried’s telling of the story isn’t all that funny, and that’s typical of the movie as a whole. It has its moments, but they tend to be sporadic, and too much of the material feels like filler, with a lot of repetition and some very modest comedic returns. That’s may have been inevitable in a picture that was shot pretty much on the fly, catch as catch can and via improvisation. But it makes for a very uneven 89 minutes. In the end one joke isn’t quite enough.

There will be those who object to “The Aristocrats” because it revels in tastelessness. But that’s really beside the point. Its real problem is just that it isn’t quite funny enough; a little of it goes a long way.