Most movie musicals, even in the Age of Glee, still face that awkward moment when somebody — say her name is “Sherrie Christian” — riding a Greyhound, bursts into “Motoring” by Night Ranger, and the rest of the bus bursts in to join her for the chorus.

Audiences today titter at that. But you measure the movie by how quickly the audience gets over that and into your musical.

“Rock of Ages,” the big screen version of the jukebox musical set to ’80s “hair metal” anthems and ballads, never does.

The all-star cast was game, but the filmmakers can’t stop winking and mocking the mockable music and the era long enough to let the picture, built around songs by Foreigner, Bon Jovi, Journey and others, work.

Seriously, you don’t let a guy who hates corn and corny film “Oklahoma!”

It’s enough to make you “stop believin’.”

Tom Cruise, as burnt-out rocker Stacee Jaxx, will do his best Axl Rose impression — bare-chested belting, waving a mike-stand bedecked in scarves — or Diego Boneta, aspiring metal singer, will tear into Foreigner’s “One Guitar,” or Alec Baldwin and Russell Brand and the rest of the cast blast “I Love Rock’n Roll,” and director Alan Shankman (“Hairspray”) will go for some cheap laugh and utterly undercut the moment.

Maybe the music, the fashion, the whole rapacious testosterone vibe of that spandex, eye-shadow, poodle-haired era is laughable. But it’s one thing to poke fun at something, quite another to attack it with utter contempt. That’s the feel here.

The film, which discards quite a bit of the book of the stage musical it’s based on, swirls around Stacee Jaxx, who staggers onstage for his farewell show at the Sunset Strip’s famed “Bourbon Room,” and prepares to launch a solo career. Sherrie, a new waitress and would-be singer (Julianne Hough) and bartender-guitarist Drew (Boneta) dream of living the rock god life Stacee leads.

But it’s 1987, and that world is about to change. The film says it’s rap and boy bands that will kill the moussed music. Ask the musicians of that era and they lay the blame on grunge and “alternative rock.”

The Bourbon Room is under pressure from the mayor’s wife (Catherine Zeta-Jones), a cross between Anita Bryant and Tipper Gore, who pledges to “clean up Sunset Strip” and “take Satan off our streets.” She and her fellow Mothers Against Drunk Rockers then kick into a rowdy.raunchy rendition of “Hit Me With Your Best Shot.”

Drew writes songs for Sherrie, Sherrie moons over Drew, but fame ruins romance in La La Land.

“The spotlight doesn’t just light them up. It’s makes us disappear,” another waitress warns Sherrie.

Thus, does Miss Innocent from Oklahoma wind up in a strip club run by Mary J. Blige, who delivers delivers what passes for a show-stopper here — “Any Way You Want it,” with a choregraphed crew of VERY athletic pole dancers behind her.

You will be amazed at the stars who take on singing, often for the first time on screen (Baldwin, Malin Akerman as a sexy Rolling Stone reporter, Paul Giamatti as Stacee’s sleazy manager) and don’t embarrass themselves. Cruise, in particular, is fun to watch and listen to.

But the songs, with a few exceptions, lack the urgency of the original renditions. You will be stunned at how leg-spreadingly crude (fitting the times, and the music) a PG-13 movie can be.

Miami was nicely dressed up for a film fantasy version of Sunset Strip in the ’80s — leather and neon and sports cars and muggers.

But seriously Adam “Hairspray” Shankman, what’s the point of making “I Love Rock’n Roll: The Musical, if you don’t.

MPAA:PG-13 for sexual content, suggestive dancing, some heavy drinking, and language

Cast: Tom Cruise, Juliane Hough, Diego Boneta, Catherine Zeta-Jones, Alec Baldwin, Russell Brand, Mary J. Blige, Malin Akerman

Credits: Directed by Adam Shankman, written by Chris D’Arienzo, Justin Theroux and Allan Loeb, based on D’Arienzo’s stage musical. 

Running time: 2:03