With all the sins one can lay at the feet of “Dirty Grandpa,” here’s one that won’t stick — false advertising.

It’s exactly what the title portrays it to be — “Grandpa” Robert DeNiro, as potty-mouthed, oversexed and politically incorrect as he’s ever been. So don’t go if you’re going to get offended by a foul-mouthed retiree indulging in a “Hangover” binge during Spring Break.

He isn’t very funny in that guise, and seeing Aubrey Plaza as a coed with Granddaddy Issues throwing herself at him with all the subtlety of a phone-sex operator isn’t quite as hilarious as seeing Plaza (she’s 31) cast, again, as a college student.

Zac Efron is along to provide the beefcake, a henpecked Atlanta lawyer driving grandpa to Daytona Beach in his fiance’s pink Mini Cooper  where the newly-widowed old man tries to score with loose women one-third his age. His long-suffering wife just died, and unknown to corporate lawyer Jason, he’s dead set on a bender.

Sex, sand, alcohol, and “amusing” encounters with a local souvenir shop/drug dealer named “Pam” (Jason Mantzoukas) ensue as they try to connect with a coed Jason knew in college (Zoey Deutch), the trashy/oversexed Plaza and their cliched gay BFF (Jeffrey Bower-Chapman).

These three are quick with a put-down, and when they aren’t, they let each other know about it.

“That was really late, but it still counts.”

“Oh? Like my period?”

We’ve already walked in on grandpa masturbating, so the bar’s set low and only dropping lower. Plaza’s coed is “half Cuban,” she cracks. “The BOTTOM half,” bending over to prove it.

Don’t let yourself get distracted with how a corporate lawyer pushing 30 could say “Shadia (Deutch) was my lab partner in photography class” and the hippy girl is somehow still in college questions.  What you’re supposed to be hunting for is laughs.

Besides, she’s attending The University of Florida. Makes perfect sense.

Jason is trying to drag this lecherous, lying drunk to Boca Raton while the old man calls him one homophobic (“lesbian”) frat boy slur (“vagina repellent”) after another and gets him into jam after jam, interrupting the future Jason’s dad (Dermot Mulroney in a thankless, embarrassing role) has planned for him.

This all takes place in locations that look very much like a pale Georgia imitation of Florida. You can see the skyline of Atlanta behind one outdoor scene. Characters mention using I-85 to transit the state (not in Florida). Yes, the Brit director, Dan Mazer, was Sacha Baron Cohen’s partner in comedy crime for years (the less talented half, judging by the continuity errors) and screenwriter John Phillips (he’s written “Bad Santa 2”) knows more about potty jokes than geography.

None of which would have mattered had DeNiro managed to make this vulgarian funny, had Efron not relied on nude or at least shirtless scenes for laughs, had Julianne Hough (as the Jewish/controlling fiance) been amusing, had the Karaoke scenes or beach body “flex” contest worked or had they not insisted on ending this with a dollop of “live the life you want:” sentiment.

That may be the grossest scene in the film, and considering the semen stain/jail rape/spiked drinks/gang fight with racial overtones stuff that’s preceded it, that’s saying something.

MPAA Rating:R for crude sexual content throughout, graphic nudity, and for language and drug use

Cast: Robert DeNiro, Zac Efron, Julianne Hough, Aubrey Plaza, Dermot Mulroney
Credits: Directed by Dan Mazer, script by John Phillips. A Lionsgate release.

Running time: 1:42