Dylan Thomas’s 66-year-old poem, “Do Not Go Gentle Into That Good Night,” shows up repeatedly in our culture, most recently ad nauseum in the 2014 film Interstellar. It’s not hard to ascertain why. Thomas’s words capture a provocative theme, outlining the inevitability of death while celebrating the struggle for survival. This theme is at the heart of last year’s debauched road film Dirty Grandpa, which stars Zac Efron and the seemingly always game Robert De Niro, but it’s poorly handled. The film buries it under a ton of lewd, gross-out material, so much so that, in watching it, you might feel like you’ve just gone skinny-dipping in a septic tank.

Yet paradoxically, Dirty Grandpa taking things too far is not what truly mars it. It’s the reverse: It doesn’t take things far enough. Although posturing as an unbridled celebration of hedonism, Dirty Grandpa is remarkably provincial and prosaic in its characters and storylines, which ultimately drains it of comedic, dramatic or intellectual worth.

In Dirty Grandpa, Robert De Niro portrays Dick Kelly, a character slightly similar to his Ben Whittaker role from Nancy Meyers’ 2015 film, The Intern. In both movies, De Niro embodies wacky old codgers who refuse to, as they say, be put out to pasture.

But while Ben Whittaker was so placid he eventually became mind-numbingly boring, Dick Kelly is a profane, hypersexual and semi-psychotic character. He’s also the estranged grandfather of Jason (Efron), a preppy, tightly-wound corporate lawyer and professional douche. Jason is on the fast-track towards marrying a horrible woman named Meredith (Julianne Hough), the type of depressing union you know is destined to end in suburbia, heavy alcohol abuse and possible carbon monoxide poisoning. Life intercedes however when Dick’s wife of 40 years passes away, and he unexpectedly asks Jason to drive him from Georgia to Florida following the funeral. When the young man reluctantly agrees, they embark on a roadtrip that meditates on life, love and the gritty particulars of old man doinking.

The road trip basically serves as a rude awakening for Jason, where he is forced to quickly confront that Dick is not the grandpa he remembers from his youth. Not only does Dick have a foul mouth, but he also loves porn, drinking heavily and has a disturbing proclivity for trying to jam his thumb up his grandson’s keister – an act he clearly finds charming but is, in fact, charmless.

He is also hellbent on getting laid, claiming to have been celibate for the past fifteen years leading up to his wife’s passing. An opportunity to take care of this arises when Dick and Jason run across a trio of hum-drum 20-somethings on the open road. This group includes Lenore (Audrey Plaza), whose apparent mission in life is to sleep with an elderly college professor; Shadia (Zoey Deutch), a woman who Jason coincidentally knows from a college photography class; and Bradley (Jeffrey Bowyer-Chapman), their gay best friend.

Ever the wrinkled horndog, Dick seizes this opportunity to pass himself off as a professor at a local university and Jason as a photographer currently working for Time Magazine. This deception ingratiates them into the group of 20-year-olds and helps establish Jason’s backstory. Apparently, he was not always a starchy, khaki-wearing ass-wipe; he once had dreams of doing photography, but put away his f-stops and light meters once that litigator money starting pouring in.

The group invites grandpa and grandson to accompany them to Daytona Beach, a city caught in the boozy grip of Spring Break. Dick agrees to this for obvious reasons: to hopefully sleep with Lenore. But Jason? It’s never quite clear. In fact, for much of the film Efron’s character is relegated to being a passive schmuck, with less agency than one of his insufferable cardigans. Eventually, he does strike up a rapport with Shadia, who wants to use her own interest in photography to study climate change. With this set-up, it doesn’t a genius cinephile to understand that the engaged Jason could be straying. Shadia might as well be wearing a big t-shirt screaming: “Your fiancée is a pitiful harpy. Choose me instead!”

Former Disney-star and professional meathead Zac Efron acquaints himself well enough with his role; although, it’s not a particularly trying part for the beefcake. Jason is basically a composite of many Efron roles from the past, and he basically exists only to suffer. The character and actor endure innumerable humiliations throughout the film, including a “flex-off” competition that looks as if it can only end in sharting and an unsavory scene where Jason passes out naked on the beach and unintentionally flirts with pederasty. Without a doubt, Efron’s most charismatic moment takes place at a karaoke bar where the filmmakers briefly relent and let him return to his crooner roots. Functioning as a nod to his work in Disney’s High School Musical series, it’s a great scene that reminds you why he became a star in the first place.

The treatment of Efron’s Jason isn’t all that surprising, as he is hardly the film’s central attraction. Director Dan Mazer and writer John Phillips seem to delight in having a living legend like Robert De Niro play Dick, and they endlessly exploit his iconic presence. From rapping Ice Cube’s “It Was a Good Day” to flopping his junk onto the pillow of Efron’s character, you certainly have never seen De Niro this way before – but that doesn’t make it good. A problem arises from the film not being as daring as it thinks it is. For all his libertinage, Dick’s behavior is driven not simply by his own hedonistic appetites, but also out of the desire to save his grandson from a life of Anglo, Ikea-based vacuousness. Additionally, Dick’s is not really a radical subversive himself, revealing a shockingly traditionalist and perhaps even patriarchal attitude by film’s end that colors all his zany senior citizen antics.

Dick’s disingenuous nature isn’t the only problem. The film simply has no insight regarding how the concept of decadence works or doesn’t work in the lives of human beings, or, at the very least, it has less than other similarly-themed entries like Spring Breakers and Pain and Gain.

Dirty Grandpa never seizes upon its fertile, preexisting thematic framework, a particularly glaring issue when you consider that the story could have explored how aging relates to concepts of decadence and pleasure-seeking. Instead, despite some strong scenes where Dick rails against the march of time and stakes his right to pursuing new forms of pleasure, the film never seriously considers this reality. Dick’s predicament of being a creepy old bastard in decline never feels authentic. This failing lies with the screenwriters, who position Dick as always confident and assured, a Nietzschian superhero, capable of kicking the ass of men a quarter his age and fucking women all night long.

Such frank unreality is part and parcel with Dirty Grandpa’s script, which is loaded with so many artificial plot mechanizations that it will make your dumb noggin spin. That’s why perhaps the most successful and communicative moment is Danny Glover’s surprise cameo as an old war buddy of Dick’s named Stinky, who Dick and Jason visit at his retirement home. This is one of the few scenes where the plot’s actual potential shines through and where the ephemeral joy and bottomless horror of existence comes to light.

The scene begins with Dick and Jason spotting Stinky, who is watching the show ALF in the rec room and screaming, “FUCK EM’ UP ALF!” Now, not only is this exclamation hysterical, but it sums up the theme you think would be given more salience throughout Dirty Grandpa. For a brief, glorious moment the film puts its comedy to work, channeling Thomas’s poem about the importance of fighting back against the slow, eroding nature of age, but it also doesn’t try to make anything more out of it than that. It doesn’t attempt to make something like mindlessly watching ALF into a conduit for redemption or a new form of healthy life. Instead, it makes space for the difficult, paradoxical concept that, when facing the inevitability of death, sometimes it makes the most sense to give in and embrace the insanity.