Grade: F

Every once in awhile a movie comes around that’s so repulsive that you leave it certain that the theatre is in need of fumigation, and get home feeling a desire for a quick shower. “Spring Breakers” was such a monstrosity, and last year “Hot Tub Time Machine 2” filled the bill. Such a picture is the abysmal “Dirty Grandpa,” in which Danny Glover briefly appears as a character named Stinky, an adjective that also fits this malodorous mess perfectly.

Glover is relatively fortunate, though: he’s embarrassed for a mere sixty seconds or so. It’s Robert De Niro who really suffers here. He was once the gold standard among American actors, whose presence was a sort of insurance policy that even if a film didn’t work, it had some respectable ambition behind it. That reputation was tarnished by roles in tripe like “Meet the Fockers,” but it’s entirely trashed here, and in the process his co-star Zac Efron reaches a new low as well.

De Niro plays Dick Kelly (only the first of many “dick” jokes), an army retiree living in Atlanta, who, on the day of the funeral of his wife of forty years, asks his uptight grandson Jason (Efron), to drive him to Boca Raton for a golf outing he would have shared with her. Jason, who works as a lawyer in the firm of his equally uptight father David (Dermot Mulroney), is about to be married in a week to prim Meredith (Julianne Hough), the overbearing daughter of one of David’s partners, but he reluctantly agrees to the trip, which he expects to be short and uneventful.

No such luck. When Jason arrives the following morning, he finds granddad plastered and pleasuring himself to porno tapes. Dick has transformed overnight from grieving widower to foul-mouthed lecher, determined to have sex to make up for the fifteen years he’s endured without it. (The word he uses, unremittingly, for the act throughout the movie begins, of course, with an “f.”) One can’t exactly say that John Phillips’ script goes downhill from there, given where it’s begun, but it certainly maintains that level of disgusting gross-out humor for the remaining running-time, as Dick makes it his mission to bed a nymphomaniac college girl named Lenore (Aubrey Plaza) they meet along the way to Florida. She’s as lascivious as Dick, and makes no bones about liking to frolic with older, or old, men.

Lenore is travelling to Dayton Beach for Spring Break along with friends—Bradley (Jeffrey Bowyer-Chapman), an ostentatiously gay black dude whom Dick enjoys belittling with monikers like “Tinkerbelle,” and Shadia (Zoey Deutch), a hippie-like do-gooder who just happens to have been Jason’s lab partner back in college, when he hoped to become a photographer. It’s not long before Dick is pushing Jason toward Shadia, convinced that marriage with Meredith will be utter misery.

That’s the movie’s move into message-making, stuff like “follow your heart” and “enjoy life.” That sort of sentimental drivel pops up every once in a while, an obviously fraudulent effort to suggest that “Dirty Grandpa” is something more than non-stop coarseness. But it doesn’t work, because the picture is 99% foul language, sleazy situations, drug humor, gay-bashing, ugly stereotyping and assorted raunchiness. The apparent assumption of Phillips and director Dan Mazer, whose slipshod work only accentuates the script’s awfulness, is that offering an endless supply of such nastiness in rapid-fire, over-emphatic style will keep your viewers content. But even here the two are cowards: after having Dick spout homophobic remarks for an hour, they suddenly show him protecting Bradley against some black gangsta types. Then, of course, they have to show that the African-American guys aren’t so bad, either. In the end “Grandpa” wimps out.

Still, De Niro joins into things with a conviction that’s almost as frightening as that he brought to Travis Bickle or Rupert Pupkin. It’s horrifying watching him engage in a “flex-off” alongside Jason, or do a karaoke rap (during which he asks for permission to use the “N” word, and gets it; that’s apparently the sign of comedic courage nowadays). But it’s still Efron who bears the brunt of the humiliation. He does one long sequence totally naked except for a stuffed animal on his penis (when a kid touches it, Jason is accused of pedophilia, of course). Elsewhere he has to wear baggy hang-me-down clown pants stained with blood and/or semen, and a G-string; and he manages to have a swastika composed of conjoined penises painted on his forehead just as he’s Skyping a rabbi. Those are just some of the indignities Efron endures for the dubious pleasure of co-starring with De Niro in this schlock. A new agent might be in order.

Mulroney and Hough are not quite as badly used, being portrayed as nothing more than stuffy prigs deserving of their comeuppance, and Deutch is attractive as the only really nice person in the proceedings (if you ever need somebody to play Julianne Moore’s younger sister, she should be your choice). But we’re back in the pits again with Plaza and Bowyer-Chapman, who ham it up mercilessly; Jason Mantzoukas, who’s cruelly unfunny and irritating as a Florida drug-dealer named Pam; Harry Zebrowski and Mo Collins, whose Keystone Kops routine mixes smarminess and vulgarity; Michael Hudson and Jake Picking, as a couple of well-muscled but dumb-as-rock lacrosse players; Brandon Mychal Smith, as a leering gangsta; and Adam Pally, whose turn as Jason’s insufferably loudmouthed cousin Nick culminates in a revelation as crass as it is unbelievable. On the technical level the movie is barely adequate; it looks chintzy and washed-out, with editing (by Anne McCabe) that’s especially sloppy, though that might just be the result of the material she had to deal with.

In fairness it must be admitted that there were some viewers in the theatre who were laughing pretty consistently at “Dirty Grandpa”—which only goes to prove that there’s no accounting for tastelessness.