Over the years, medical there have been a variety of crude comedies that try to elicit laughter through gross masturbation sequences and relentless jokes about the male and the female anatomy. The thing — the enormous difference between many of those films and Dirty Grandpa, the newest entry in this outlandish genre — is Robert De Niro. De Niro, a fearless actor, a two-time Oscar winner and an amazing performer, stars as the title character in this new film. The big question that comes to mind after seeing the finished film is why he said yes to this crude comedy.

Within moments of the film’s opening sequences, Dick Kelly (De Niro) — who has recently lost his wife after a long battle with cancer — masturbates to a porn video and isn’t shocked when his obviously-horrified grandson Jason (Zac Efron) walks in. It would be hard to say that the movie doesn’t improve from there (how much lower can it go?). It does but it never manages to outgrow its sophomoric comedic roots.

Dick barely has time to mourn for his wife — who he says he loved endlessly — before he decides to recruit Jason for a road trip from Georgia to Florida. Jason is an engaged professional lawyer whose marriage to his cold-hearted fiancé Meredith (Julianne Hough) is only a few days away. After his grandfather guilts him into saying yes, Jason decides to accompany the patriarchal man he once loved spending time with.

To his surprise, that man no longer exists. Instead of the generous grandfather he once knew, he finds that his grandfather has become an obnoxious and sex-crazed pervert who wants to have unprotected sex with any young woman he can find.

De Niro seems to be enjoying himself here as he undercuts the tough guy character he’s played so many times before. This isn’t the De Niro we’re used to. Unfortunately though, his character is one of the most vulgar and obnoxious characters we’ve ever seen him play. The actor has performed in some worthy comedies in the past (in movies like Meet the Parents and Analyze This) but those films worked because the punchlines were stronger and better-written than any of the sex jokes here. His character here is a one-note jerk whose behavior is horrifying and shocking to many of the people he meets.

Efron here is also playing against type in beginning the film as a straight-laced corporate lawyer who is far more conservative and respectable than his horny grandfather. This is a far cry from the frat boy he played in Neighbors or the self-absorbed jerk he played in That Awkward Moment. One character even calls him a “Mitt Romney Terminator” when he’s angry. Of course though, this character is inevitably dragged into parties and craziness by his free-spirited grandfather, who wants him to become the idealistic but party-crazed teenager he once was.

Once Jason reunites with his college classmate Shadia (Zoey Deutch) and Dick starts flirting with her friend Lenore (Aubrey Plaza), it’s hard not to know where the story is going. Yes, this movie– which features ninety minutes of debauchery and sex jokes, homophobic puns and Nazi references — wants to end with a lesson to the audience.

After all the mayhem and the crudeness, there’s supposed to be a real takeaway for the audience. The lesson that the filmmakers intended is about staying true to yourself and not succumbing to societal pressures. The only lesson I learned though is that people thinking about going to see this movie should stay home.