There's basically one joke behind the power duo Tenacious D: watching Jack Black say "Rock" while overemphasizing the end consonants and widening his eyes, the gap between his chubby face and his rock-hero ideals half the fun. For (the fictional version of) Black and partner Kyle Gass, the very idea of rock -- or, more accurately, "The Metal," which, as the end credits song claims, could not be killed by grunge, punk, new-wave or techno, smiting them all to the ground -- is the conduit out of their sad, dispiriting lives. Yet Tenacious D set Black on his path to stardom, the D has released a successful album that even got radio play, and now (too late, as always) a movie. Inexplicably, Tenacious D in The Pick of Destiny chooses to follow the lead of every comic-book franchise ever, providing an origin story where none was really called for.

The Pick of Destiny begins with a way out-of-date parody of the THX ads that used to play before movies in the '90s, back when that was still state of the art. Here, little animated versions of Black and Gass come out, get the requisite first weed and fart jokes out of the way in the first 10 seconds, and finally a notice appears: "THC: The Audience is Buzzed." As a competent, sober critic, I knew to expect something like this, but I still showed up to the screening straight out of sheer professionalism. My mistake.

With a plot basically grafted over the mother of all stoner-fests, Up In Smoke (a road trip en route to a musical contest, with plenty of pot jokes along the way), The Pick of Destiny strings together a bunch of half-baked gags (in both senses) as Black and Gass learn about the titular pick (made from Satan's tooth, with the power to grant awesome shredding abilities to all who possess it) and set out to steal it from the Rock and Roll History Museum. Then they can write a masterpiece, win an open mic contest and pay their rent. This is a coherent plot summary.

Amiable and toothless, it all plays like nothing so much as an extremely belated rip-off of Wayne's World, except less self-aware and with Dio instead of Alice Cooper as the rock god of choice. The unimaginative prevails (the theft is lifted directly from Ocean's 12), although the finale should be mandatory at clip parties: Suffice to say that a rock-off between the D and the Devil (Dave Grohl) is pretty much the only thing here that's as awesome that as it sounds like. Kyle Gass makes a pretty good foil insofar as you don't normally see a straight man that's this passive most of time; instead of being aggravated by the manic Black, he tempers him. But you can never steal the spotlight away from Black, and neither Gass nor director Liam Lynch (who totally botches his one chance to shine, the mushroom trip sequence) attempt to do so.

The great thing about rockists and metalheads is that their tastes don't change; it's easy to make them laugh the same way they did 20 years ago. If the thought of Black singing "Rock is not the devil's work/It's magical and rad" is enough to make you giggle, get ready to laugh: The jokes here would've made just as much sense in the '80s. Or more sense, really; part of the joke of Black's turn as the metal mentor in School of Rock was how out of touch he was with the kids. Here, with no real oppositional force (like many stoner movies, this one assume that pretty much everyone, including would-be adversaries like security guards, is also perpetually stoned), his comedy falls into a vacuum. And while it's not an actively unpleasant place to be, you don't actually need to see the movie to know your response to it.