A blistering satire of both heavy metal music and the rock documentary genre, This Is Spinal Tap counts as one of cinema’s most potent, side-splittingly funny, comedies of all time. Every joke, every sight gag, every parodic skewering lands with such pitch-perfect comedic timing that it’s hard to believe it was all improv and no script.

Once lauded as “one of England’s loudest bands,” heavy metal outfit Spinal Tap is found to be far past its (modest) peak, struggling to attract an audience and on the verge of breaking up. A documentary crew chronicles their latest album release, which flops, and the accompanying tour, which lurches from one hilarious crisis to another.

Cast members Christopher Guest, Michael McKean, and Harry Shearer are so committed to authenticity that they actually play their own instruments and write their own songs, and even toured for real as Spinal Tap following the success of the “documentary” about the band.

Meanwhile, director Rob Reiner, who plays documentarist Marty Di Bergi (a deliberately clumsy portmanteau of Martin Scorsese, Brian De Palma, and Steven Spielberg), expertly and methodically deflates the pretensions of the documentary form.

The only film to dial it up to 11, This Is Spinal Tap remains a stone-cold classic.