Adam Sandler rarely goes wrong underestimating his audience. There's a mild disappointment like "Jack & Jill" here or an outright flop like "Little Nicky" there, but otherwise Sandler enjoys one of the most commercially consistent careers in Hollywood.

He's at his best when he works with a serious filmmaker on an offbeat project (Paul Thomas Anderson's "Punch-Drunk Love," Judd Apatow's "Funny People"), but he's savvy enough to know that's not what his audience really wants to see, and he doesn't do it often. Instead, his Happy Madison brand continuously cranks out mild variations in the same sub-juvenile strain.

If you've seen one, you've seen them all: funny voices, fart jokes, men getting hit in the testicles, busty women in tight shirts or swimsuits, very young and very old cast members dropping age-inappropriate dialogue, overweight people mocked and celebrated for their size, obnoxious cameos from Sandler buddies like Rob Schneider, Nick Swardson and David Spade, etc. etc. And then, inevitably, a third act wrapped up with a grossly sentimental bow on top. Because in the end every Sandler movie, no matter how stupid, has to have heart.

"That's My Boy" never departs from the template, but does make one minor but important tweak to differentiate it from the rest of Sandler's Happy Madison vehicles: it's rated R. This is Sandler's attempt to crash "The Hangover" party, and it will be interesting to see how his audience responds.

Of course, the movie itself isn't actually any more interesting. Although Sandler is working with a new director -- "Sex Drive" writer-director Sean Anders -- and the film has a little more visual pizazz than the sloppy standard established by Happy Madison favorites Dennis Dugan and Frank Coraci, Sandler's entry into the world of raunch is as middling as you'd expect.

There are signs of an edgier comedy here, and "That's My Boy" is built on a particularly tasteless premise. When Sandler's character Donny Berger was barely a teenager he had a sexual relationship with his teacher (Eva Amurri Martino). The movie treats this like a naughty joke -- young Donny isn't a victim because he's living out the fantasy of sleeping with a hot teacher. And while Amurri is as alluring as ever, watching her hit on adolescent co-star Justin Weaver is awkward and embarrassing at best, utterly repellent at worst. But funny? Nope.

It would take filmmakers considerably sharper than Anders and writer David Caspe (TV's "Happy Endings") to pull this off. Maybe, John Waters could've done it in his prime. Gregg Araki did his most mature work exploring sexual abuse with compassion, complexity and some degree of humor in "Mysterious Skin." No one would expect the same from a Sandler movie, but that probably means a Sandler movie shouldn't even try.

"That's My Boy" uses the teacher-student sex as "outrageous" set-up for a more traditional father-son bonding story. The teacher gets pregnant and Donny grows up into a deadbeat dad -- he was too young and irresponsible to properly raise a kid and the teacher landed in jail when their relationship was discovered. Donny's son (Andy Samberg) distanced himself from dad as soon as possible, changing his name from Han Solo Berger (hilarious, right?) to Todd Peterson and cutting off all communication. Donny has no clue where his kid is, until he sees a wedding issue cover of Parade magazine featuring Todd and fiancée Jamie (Leighton Meester).

This sets Donny on a course to win back his son's affection for reasons both selfish (he stands to make good money if he can sell a reunion with his son and the teacher to a sleazy talkshow) and good-hearted (he loves his boy!). Those motivations will eventually come into conflict with each other, Donny will have to make a choice and... well, even if it's R-rated, a Sandler movie's gotta have heart.

The question is what does a Sandler movie get to have with a R rating? The answer is relatively banal: aside from the teacher-student creepiness, the middle finger becomes a punchline of choice and there's more nudity and sex jokes than usual. Donny frequents a strip club, where the star performer is played by plus-sized fiftysomething comedienne Luenell scantily clad in lingerie and a pair of pasties. There's more flesh-baring comedy throughout -- both male and female, physically fit and not -- and gags involving masturbation, semen and several unconventional sexual relationships. One late breaking twist seems deliberately designed to overshadow the farcical treatment of statutory rape.

The movie earns its R, but there's always something holding it back. I think it's Sandler's genial sensibility. He's never going to be as nasty as Todd Phillips or as warped as Jody Hill and David Gordon Green. He doesn't need to be. But to get interesting, "That's My Boy" could've used less of Sandler's childishness and more of someone willing to push it in a darker, more dangerous direction.

It certainly doesn't gel as a mismatched buddy comedy. Samberg plays Todd as a one-note uptight cuckold -- as much a patsy of Meester's domineering shrew (would you expect any other kind of female lead in a movie like this?), as a victim of his father's absentee parenting. It's a largely dull and irritating performance, which is either a reflection of Samberg's lack of movie star charisma or simply a byproduct of very bad material.

You don't usually walk out of a Sandler movie praising the performances, and that's especially true here. The supporting players range from competent sketch comedy types -- Will Forte, Rachel Dratch, Ana Gasteyer -- to cringeworthy stunt castings -- Milo Ventimiglia as Meester's militant military brother, James Caan as an unruly Irish priest, Vanilla Ice as himself. None of them leave a lasting impression.

Only Sandler is entirely in his element, and he's long ago proven criticism of his man-child schtick irrelevant. You have three choices: Give in and go with the nonsense, pretend that his films have hidden subtext and deep meanings (as Armond White usually does), or simply ignore. Love him or hate him, that's our Sandler.

"That's My Boy" opens in theaters June 15