Among the famous people who make cameo appearances in the new Adam Sandler comedy “Jack and Jill”: Johnny Depp, John McEnroe, David Spade, Shaquille O’Neal, Drew Carrey, Christie Brinkley, Michael Irvin, Regis Philbin, Dana Carvey and even Jared Fogle, the guy from the Subway sandwich commercials.

Total number of laughs all this amassed star power generates: One.

The bit with Depp, who has an amusing exchange with Al Pacino, made me chuckle. Yes, Pacino is also in “Jack and Jill,” playing himself. This is not a cameo but a real supporting role. And unlike Robert DeNiro, who often sleepwalks through his for-the-paycheck jobs, Pacino gives the movie his all. Method is Method, whether you’re working with David Mamet or Dennis Dugan.

Dugan is a TV and film (mostly TV) actor who has directed many of Sandler’s pictures, from “Happy Gilmore” to “Big Daddy” to “You Don’t Mess with the Zohan.” Why isn’t Dugan better-known, considering his track record of box office hits?

First, because he’s terrible at his job (this movie looks so cheap and crummy that when Sandler attends an L.A. Lakers basketball game, all you can notice is the actor standing in front of a green screen, the athletes behind him pasted in by computer.)

But Dugan isn’t bad enough for anyone to remember. And he is practically invisible as a director anyway. He’s a yes-man who is good at doing what he’s told.

“Jack and Jill” contains long stretches of squirm-inducing tedium in which Sandler riffs and ad-libs far longer than he should, as if he thought that wearing a dress would immediately turn anything he did into comedy gold.

Why didn’t anyone on the set (or even the editing room) tell him how irritating he was?

Playing Jack Sadelstein, an L.A. ad exec dreading the annual holiday visit of his twin sister Jill (also Sandler), the actor is obviously having fun. But the party doesn’t include the audience.

The film radiates a smirking, self-satisfied vibe, and Sandler goes so far over-the-top as Jill — a whiny, needy New Yorker who has never used a computer, has never eaten Mexican food and, apparently, has never gone out on a single date — that I was gritting my teeth 15 minutes in.

Sandler is a capable actor: He’s done good, sometimes surprising work when he’s paired with a strong director (Judd Apatow’s “Funny People,” Paul Thomas Anderson’s “Punch-Drunk Love,” Mike Binder’s “Reign Over Me,” James L. Brooks’ “Spanglish”). But left to his own devices, Sandler reverts to his worst, laziest habits.

He forgets that what might have been tolerable in a three-minute “Saturday Night Live” skit becomes excruciating when stretched to feature-film length. And this is one of Sandler’s PG-rated, kiddie-friendly films, so instead of any edgy humor, you get fart jokes, pratfalls and more fart jokes (I counted four, but there could be more).

I might not have been able to make it all the way through “Jack and Jill” if it weren’t for Pacino — not because he’s funny but because his performance is fascinating. This is arguably Pacino’s first big sell-out, but he earns every single dollar. He plays himself as an arrogant, show-off manipulator who pitches a fit onstage when someone’s cell phone goes off during a performance on Broadway; talks to his service staff in gibberish to make people think he can speak foreign languages; and relentlessly pursues Jill as a way of getting into character for an upcoming gig as Don Quixote in “Man of La Mancha.”

Pacino doesn’t hold back, whether he’s prancing around to “I’m a Believer” or pillaging famous lines from his most revered characters for laughs (he breaks out “The Godfather” and “Scarface,” too).

Why isn’t he as irritating as Sandler? Because in a comedy pitched at such a high volume, even Shouty Al fits right in. More importantly, Pacino isn’t trying to be funny: He plays everything completely straight, and that’s what draws your attention. At the end of the film, when he watches the song-and-dance TV commercial for Dunkin’ Donuts that Sandler’s ad-man convinced him to do, he’s understandably horrified. “Burn this,” Pacino says. “No one can ever see this.”

The joke, of course, is that he’s also referring to “Jack and Jill.”

Except by then it’s too late: He, Sandler and Dugan have already taken your time and money, along with what probably was a hefty check for product placement from Dunkin’ Donuts.

In “Jack and Jill,” the biggest joke of all is on you.