Westport News film critic Susan Granger reviews the new move, “Dirty Grandpa.”

I’m fairly certain that this wannabe comedy is one of the most dreadful films Robert De Niro has ever made, if not the worst. And the scene in which the two-time Oscar-winner masturbates to porn has got to be the most humiliating of his career.

De Niro plays a recently bereaved widower who cajoles his uptight lawyer grandson, Jason (Zac Efron), into driving him from Atlanta to Boca Raton. It’s the week before Jason is scheduled to marry demanding, obsessively controlling Meredith (Julianne Hough), but he reluctantly agrees.

As soon as they hit the road in Meredith’s pink Mini-Cooper, Grandpa confesses that he’s been celibate for 15 years and is determined to get laid. Not surprisingly, they meet up with three college students.

Shadia (Zoey Deutch) knew Jason from photography class and Lenore (Aubrey Plaza) has a yen for older men, meaning Grandpa’s “in like Flynn,” as they used to say, referring to Errol Flynn’s legendary prowess with women. Bradley (Jeffrey Bowyer-Chapman), their gay African-American buddy, becomes the target of Grandpa’s racist, homophobic insults.

After a brief detour to visit Grandpa’s old Army buddy (Danny Glover), they all hook up in Daytona Beach, where drugs and bikini-clad babes reign supreme.

Obviously attracted to Shadia, Jason inadvertently smokes crack and collapses on the beach. With penises shaped like a Nazi swastika inked on his forehead and naked except for a plush toy on his genitals, Jason is then mistakenly accused of child molestation.

Adding to the embarrassment, Dermot Mulrony plays Jason’s lawyer father, Adam Pally is his idotic cousin and Jason Mantzoukas is a zany drug dealer, working alongside a couple of complicit, corrupt Florida cops (Henry Zebrowski, Mo Collins).

Screenwriter John M. Phillip, whose claim to fame is writing skits for Sacha Baron Cohen, contributes relentlessly filthy vulgarity, sketchily directed by Dan Mazer. The primary running gag involves Grandpa sticking his finger in Jason’s butt. And don’t confuse the title with Johnny Knoxville’s mischievous “Bad Grandpa.”

On the Granger Movie Gauge of 1 to 10, “Dirty Grandpa” is a tedious, testosterone-propelled 2 — raunchy, repellent and desperately not funny.

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