It’s not the best joke in the world, but if it’s told right, it’s the dirtiest joke in the world — and it’s the entire premise behind “The Aristocrats,” the new documentary by Paul Provenza and Penn Jillette.

The reality of comedians talking about comedy is rarely entertaining, but in this case it’s hysterical.  Several dozen comedians — you’ve heard of many, never heard of some — both tell and dissect the same joke.  There’s a setup, a punchline, and a completely improvised middle section, which is where the joke teller lets loose with a string of supremely sexual and scatalogical acts and descriptions far beyond anything you’ve ever heard before.  It’s disgustingly brilliant.

What takes it to that level is not just hearing the joke told every possible way, including a funny twist by Carrot Top, a card trick version by sleight-of-hand artist Eric Mead, and even one by a mime.  It’s also hearing the variations on the joke that turn it inside out and upside down (I particularly enjoyed the adaptations by Wendy Liebman and Martin Mull).  Adding to the effect is the rhythm — the comedic timing of the editing that keeps it all flowing.

It’s not playing in thousands of theaters, so “The Aristocrats” won’t rake in the kind of documentary bucks that Michael Moore or emperor penguins can — in St. Louis, it’s only showing at The Tivoli, where the manager told me that it’s their best-attended movie in a very long time — but I suspect that when it comes out on DVD, it will become must-see viewing in many homes and dorm rooms across America (that DVD will hopefully include much more material that they couldn’t stuff into the theatrical release from the hours of footage they shot — while it’s great to see Kevin Pollak doing Christopher Walken telling the joke, I want to see the Kevin Pollak doing Albert Brooks version!).

However, if you’re going to see it, please remember that these are only words — pure free speech — no one was injured in any way by making or seeing “The Aristocrats,” and there are no graphic visuals of any kind (unless you count seeing Phyllis Diller in a sleeveless dress).  Still, don’t go see it if you’re easily offended, because you’ve been warned.

On the other hand, if you want to see funny people being funny and raunchy and clever and insightful all at the same time, don’t miss “The Aristocrats.”

Memo to Paul and Penn:  not only did you do a good job rounding up more than the usual suspects and compiling their versions of the joke, but you added a very nice touch with the dedication at the end of the credits.

Bonus: On “The Aristocrats” website you’ll find Penn’s blog going all the way back to November, 2001, when they first starting visiting all the comedians, getting them on tape, hanging with them, and other behind-the-scenes stuff.  It’s apparent this was a labor of love, and Penn lays out all the respect these comedians deserve.