Comedies come in all shapes and sizes. A special few hit their targets throughout, earning giant laughs while telling a story to care about and characters worthy of our interests. Some allow us to consider an idea or a viewpoint we hadn't before, or provide a mirror for ourselves to gaze into even as we chuckle. Some are more sweet or satiric than hilarious, and some are simply big entertainments without being all that deep. A lot of the time, comedies can be middle-of-the-road mediocre, neither offensive nor particularly memorable. Every once in a while, there is a really bad one that somehow doesn't succeed in its humor or as a fun time. And then, only once, maybe twice per year, a theatrically released comedy comes along that goes so wrong in every way it is impossible to reconcile how it could possibly have gotten made by human beings and seen the light of day. In 2015, no comedy appalled as greatly or as consistently as the mean-spirited, intolerant "The Wedding Ringer." In 2016, this head-scratching cinematic anomaly belongs to "Dirty Grandpa," a movie so annoying, so ugly, so lead-footed, so misguided, and so blisteringly unfunny it has to be seen to be believed. Please don't see it, though. It's not worth the sacrifice.

Jason Kelly (Zac Efron) may only be in his twenties, but he has a solid head on his shoulders and an enthusiastic burgeoning profession as an attorney at dad David's (Dermot Mulroney) law firm. He is mere days away from marrying Meredith (Julianne Hough) when his grandmother passes away from cancer. When, at the funeral, Meredith steals away his attention to ask him if he prefers to wear a coral or salmon-colored tied at their wedding, it may be a red flag she is not quite the perfect lifetime mate for him. Nevertheless, nuptial preparations are going full speed ahead until Jason's outspoken grandfather, Dick (Robert De Niro), requests his grandson accompany him for a quick trip to Boca Raton, Florida, where he and his late wife vacationed every year. Once en route, Jason discovers Dick's ulterior motive: having not been with another woman in fifty years, he is determined to get laid. When they meet a trio of college kids headed to Daytona Beach for spring break—among them, coincidentally, Jason's former classmate Shadia (Zoey Deutch) and the sexually voracious Lenore (Aubrey Plaza), who wants to ravage Dick—their road-trip destination abruptly shifts. The usually responsible Jason is about to get an education in how quickly letting loose can get him into a world of trouble.

Directed by Dan Mazer (2013's likable revisionist romantic comedy "I Give It a Year") and written by John Phillips, "Dirty Grandpa" is tone-deaf, hostile and endlessly unpleasant. There is a fine line between ribald and unremittingly obnoxious, and this film crosses it in the first scene and stays there for an unbelievable 108 minutes. In a race to humiliate every actor involved, Mazer and Phillips have created a conveyor belt of caricaturized human monstrosities for them to portray. No one escapes unscathed, though in a different movie set on a planet more closely resembling Earth, Zac Efron's (2014's "Neighbors") Jason may have been a suitable protagonist. The movie's thesis presupposes that Jason is an unhappy guy who has given up his love of photography for a career in law, and who is about to make a big mistake if he goes through with his marriage to Meredith. This latter observation may be true, but the former one does not take into account that he genuinely appears to enjoy being a lawyer. Moreover, just because he works as an attorney doesn't mean he still can't take pictures. Dick wants his grandson to give up his focused grown-up life and instead party so hard he is arrested twice in two days. None of this makes any sense.

The rest of the characters are the kind of people you wouldn't just cross the street to avoid in real life, but would take a detour around the city so you wouldn't have to be in their general vicinity. Robert De Niro (2015's "The Intern") embarrasses himself as the interminable Dick Kelly, put into situations less amusing than simply depressing (the sight of him pleasuring himself to a porno is the kind of raunchy gag without a punchline only 12-year-olds would find a laugh riot). Unfiltered in an off-puttingly aggressive way, he objectifies every woman he meets and nonchalantly spits out homophobic remarks directed at Shadia and Lenore's friend Tyrone (Brandon Mychael Smith), then later hypocritically lectures someone about not discriminating against him. A heart-to-heart talk Dick shares with Jason where he waxes philosophic about his manly urges to have sex with anything that moves is meant to give the viewer insight into his motives, but only serves to make him seem all the more sad and miserable.

The usually effervescent Julianne Hough (2013's "Safe Haven") is trapped in the offensively thankless role of Jason's controlling fiancée Meredith, a self-involved, Type-A personality with few redeeming qualities. A key reveal late in the picture involving her character is reprehensible, an illogical discovery shoehorned in to make her even less sympathetic than the horror show she already has been established to be. As Jason's eventual love interest, the supposedly more down-to-earth Shadia, Zoey Deutch (2013's "Beautiful Creatures") isn't exactly ingratiating; she is introduced by covertly stealing from Jason and using the money on his table to pay for her diner bill. A lot of Dick's negativity is leveled at his son, David, for being uppity and humorless, but there is no actual evidence of either of these things. Dermot Mulroney's (2015's "Insidious: Chapter 3") part asks that he have nothing to do except run around in the third act with a half-dozen penises drawn on his face. If any performance shows a modicum of promise, it is Aubrey Plaza's (2014's "Life After Beth") goofy, uninhibited turn as Lenore. Sadly, this character might be the most over-the-top exaggeration of them all, a smiley nymphomaniac who has only one thing on her mind throughout (hint: it isn't Dick's personality). Worse still, Plaza is stranded by a hopeless script that treats her like a gimmick instead of a person.

"Dirty Grandpa" has no point, no sense of comic timing, and no jokes clever enough to be considered jokes at all. Supporting characters include a conspiracy-theorizing cousin (Adam Pally) who makes a scene at his grandma's casket, a pair of inept cops (Mo Collins and Henry Zebrowski) who give Jason a pair of semen-coated pants to wear out of jail, a drug-dealing store clerk named Pam (Jason Mantzoukas) who thinks nothing of shooting up his own store because, after all, it's Florida (har, har!), and a beefy but barely overweight college jock, Brah (Michael Hudson), whose sole purpose for existing is so he can be on the receiving end of a stream of fat put-downs. Toss in insults directed at gay characters and the offensive use of a disabled person whose disability is meant to be the pinnacle of comedic hilarity, and what we have is an absolutely disgraceful assault on its genre. "Dirty Grandpa" is painful, charmless and cruel, carrying a bleak outlook on humanity legitimately alarming to behold. Even viewed as nothing more than a frivolous trifle, it is stomach-churning in its contempt for audiences.