Adam Sandler embraces all of his worst habits in “Grown Ups 2.” (Tracy Bennett)

Nearly every Adam Sandler movie seems to provoke handwringing over whether he’s living up to his potential. He’s capable of portraying nuanced characters, as he did in “Funny People” and “Punch-Drunk Love,” but he’s clearly happy to settle for his go-to routine of acting like a child and spewing lazy jokes that include his comic holy trinity: bodily fluids, flatulence and ogling scantily-clad women.

The shtick must be rote by now, and, indeed, “Grown Ups 2” appears to have been made while engaging as few brain cells as possible.

The movie revisits the group of longtime friends that made “Grown Ups” a hit in 2010, bringing in $162 million at the domestic box office. That impressive, if depressing, sum shows the hunger for senseless summer comedies. But “Grown Ups 2” isn’t merely mindless. At times it seems to actually drain IQ points from its viewers while wasting a talented cast of “Saturday Night Live” alums, who are all capable of being much smarter and so much funnier.

The film follows four men (Sandler, Kevin James, Chris Rock and David Spade) over a single day as the quartet plans a 1980s-themed summer kickoff party. But every man also gets his own individual story line, each of which seems plucked from a bad sitcom. Sandler’s Lenny is dealing with the fact that Roxanne (Salma Hayek) wants another baby; Kurt (Rock) gets to lord over Deanne (Maya Rudolph) that he remembered their anniversary and she didn’t; Eric (James) has to hide frequent trips to his mom’s house from Sally (Maria Bello); and Spade’s Marcus finds out he fathered a son, who happens to be a tattooed teenage thug.

All these threads, plus many more involving the younger generation’s love lives, math deficiencies, sports aspirations, broken bones, dirty diapers and bullying, vie for attention over the course of the relatively short run time. Throw in a crew of frat boys, led by Taylor Lautner, who aim to destroy the middle-aged men, and you’ve got one overstuffed film that only a runaway elk can resolve.

Sandler must be adept at remembering to cash in on IOUs to assemble this crew of actors. At one point, Hayek, Rudolph and Bello have to act idiotic enough to believe a skeevy janitor (played, naturally, by Jon Lovitz) is their aerobics instructor, and they comply when he orders them to turn around, bend over and spank themselves. Female objectification never looked so stupid.

The fact that some moments are genuinely laugh-out-loud funny almost makes the whole endeavor sadder. Each of these comedians shows how capable they can be of transcendent physical humor, and even Shaquille O’Neal, who plays a cop, lands some good lines. Why do writers Sandler, Tim Herlihy and Fred Wolf have to sully those moments with jokes about a potbellied man in a too-tight T-shirt eating his own belly button lint? Why the need to forever spoil chocolate frozen yogurt with an inane and grotesque spectacle of toilet humor?

Ruining a beloved dessert isn’t Sandler’s worst transgression, however. That would be the way his movies make a movie critic feel like an old curmudgeon, muttering to herself: Seriously, Adam, grow up.

“Grown Ups 2”

r ½

PG-13. At area theaters. Contains crude material, language and bare backsides. 101 minutes.