This Is Spinal Tap at 40: the note-perfect rock satire still goes up to 11

The bands that come together organically, without the aid of want ads or tear-off flyers stapled to telephone poles, are generally catalyzed by a mixture of chemistry, inspiration and boredom.

Related: This Is Spinal Tap at 35: the faux-rockers reunite at Tribeca film festival

A few guys – more often than not, it’s still guys – hang out, realize they get along, bond through their overlapping tastes, and then grow fidgety to do something about it. Screwing around becomes noodling, noodling becomes jamming, jamming becomes something that can be passed off as a performance in exchange for beer money. For so many of the greats, rocking began as a gratifying, potentially lucrative way to goof off with one’s friends, their childhood spirit of play aged up from games to music; we can see the natural camaraderie in everything from the laddish pranksterism of A Hard Day’s Night to the hijinks on Boygenius’s social media channels. Such intimacy powers the alchemy activated when locking into a groove, an instinct-based communication coordinating several minds on a shared creative frequency. It’s one of the closest things to magic that exists on Earth.

A less-cool cousin of this phenomenon takes place when improv comics hit the sweet spot, wordlessly dialed in to each other’s thinking as they forge a path through a scene together. They won’t let you forget the similarity, either; it’s an old line that every comedian dreams of rock stardom, given away by the vernacular of “gigs” and the handmade DIY posters and the occasional shared bill with one of their college-radio heroes. Credit where it’s due, then, to Michael McKean and Christopher Guest, who managed both. Their crowning collaboration, This Is Spinal Tap, which pelvic-thrusted its way into cinemas 40 years ago today, has received rightful acclaim for the precise fidelity with which it re-creates eras and genres. The parody songs work so well because they’ve been written and mixed to sound just like the genuine article, but the film also remains a classic in part for the equal authenticity its creators brought to the band dynamic. Beneath the soundbites quoted all the way to 11, there’s a close-knit clique of simpatico doofuses trying to crack each other up, and laying waste to the rest of us in the process.

Guest and McKean met as well-heeled New York whippersnappers during their college years in the late 60s, their orbits connected by a mutual interest in lyrical humor. Born to posh parentage with roots in British government, a young Guest received classical training on clarinet and mandolin, plucked the six-string with boyhood classmate Arlo Guthrie, and penned note-perfect parodies of Bob Dylan and James Taylor for the National Lampoon Radio Hour; raised by one of the co-founders of Decca Records, McKean cut his teeth as axeman for the “Bach-rock” baroque pop outfit The Left Banke. His set of skills landed him a name-making role on Laverne & Shirley alongside his school chum David Lander, the breakout popularity of their characters Lenny and Squiggy leading to the release of a faux album as Lenny and the Squigtones. The liner notes credit guitar work from one “Nigel Tufnel”, a pseudonym Guest would revive for a TV pilot shot around this same time with director Rob Reiner and Harry Shearer, one of McKean’s buddies from the LA comedy troupe the Credibility Gap.

The show tentatively titled The TV Show never took off, but they’d laid the groundwork for what would eventually mature into the thoroughly immature proto-hair-metal five-piece Spinal Tap. “It’s such a fine line between stupid and clever,” muses McKean as David St Hubbins, giving the project its unofficial mission statement. This cadre of chauvinist numbskulls – David and Nigel as the feuding John and Paul with Shearer’s Derek Smalls their peacemaking Ringo, backed by a rotation of constantly perishing drummers – dispensed small jewels of absurdism so wrapped up in the logic of their own idiocy that they circled back to brilliance. They tinkered with the quirks of language like melodies, talking themselves into a dead end as if to remind us they were making it all up as they went: “It’s like, how much more black could it be? And the answer is none. None … more black.”

After the millennium, the winning strategy of gathering funny people and letting them do their thing would lead to the bloat and indulgence of the Apatow Company, a far cry from the rigor and economy of Reiner’s techniques. The mockumentary structure lent itself to setups and punchlines, each segment in its lean-and-mean 82-minute run time sketched along the path to the laugh. The lightweight maneuverability of Reiner’s handheld 16mm camera afforded spontaneity to his cast, allowing their riffing to open up and breathe. The bit players – Fran Drescher as publicist extraordinaire Bobbi Flekman, Fred Willard as a squaresville air force lieutenant, real-life bandleader Paul Shaffer as “the incompetent promoter Artie Fufkin” – seamlessly integrate themselves like great session musicians sitting in with the group for a number or two. The McKean-Guest-Shearer-Reiner brain trust sharing written-by credit never met a sight gag they didn’t like; there’s a faint hint of Wile E Coyote in the escalation of tools used to extricate Derek from a large amniotic egg that won’t open, a crescendo from pliers to blowtorch.

From the top of the charts to opening for a puppet show, the rising and falling fortunes of Spinal Tap reiterate a familiar showbiz arc, dotted with behind-the-music tropes including the Yoko-esque girlfriend exacerbating intra-band tensions and the long-suffering manager permanently at the end of his rope. The film likewise spoofs specific corners of pop-cultural output, with Spinal Tap’s pivots from Ed Sullivan-era Beatles to floral psychedelia to testosterone-fueled cock-rock casting them as shameless trend-chasers. They have this much in common with their spiritual son Dewey Cox, though the film’s closest descendant would have to be Popstar: Never Stop Never Stopping, which also drew on the long-honed rapport between true friends for an industry cautionary tale about remembering who your people are. Guest would stick by his as he took the director’s chair in the 90s, enamored with his stable of oddballs good on their feet. His breakthrough Waiting for Guffman profiled another collection of the clueless bonded by the pleasure they take in putting on a show together, an ensemble playing for a pathetic love of the game rather than chicks and money. But it was never really about that for Spinal Tap, either. One gets the sense they and the men playing them do this mainly for each other, and that it’s our privilege to hang out too.