The pantomime season is upon us, and anybody seeking clumsy festive slapstick set to a thunderous soundtrack of mock-heroic metal could do worse than Tenacious D. Yet, like most pantos, you may find the rudimentary humour a somewhat guilty pleasure and have no wish ever to return.

Jack Black and Kyle Gass have been playing the part of "the D" since 1994, way before High Fidelity and School of Rock catapulted Black into the Hollywood stratosphere. The initial gag was that the pair were hopeless losers, an acoustic metal duo convinced they were the greatest band on earth despite the indifference of the wider world.

Two albums and a movie down the line, Tenacious D have fetched up at some point roughly equidistant between Spinal Tap, Wayne's World and the Darkness. Crammed with hoary power chords and corny skits, tonight's hyper-ironic rock opera is utter guff but, in its defence, makes no less sense than Ben Elton's Queen musical We Will Rock You.

When it's tolerable, it's because Black and Gass have a patent love for what they do. Both are competent musicians, and Black is a gurning, twitching presence who carries the night's one joke by sheer force of personality; it's hard to imagine any other Hollywood A-lister bothering to do this stuff. Black is funniest at his most puerile, adopting a warbling Axl Rose falsetto for the epic gibberish of Kickapoo: "'Twas I who fucked the dragon/ Fuckalize sing fuckaloo". Master Exploder is a cleverly dumb rock odyssey and is, in truth, no sillier than Metallica.

Dude, it's more fun than Dick Whittington at the local Rep, but it's hard to see where Black and Gass can take it next.