Starring: Robert De Niro, Zac Efron, Zoey Deutch
Directed by: Dan Mazer (“I Give It a Year”)
Written by: John Phillips (debut)

Although comedy is not the first thing one would think of as a cornerstone of Robert De Niro’s illustrious career, the two-time Oscar winner has had a few moments of levity with performances in films like “Meet the Parents” and “Silver Linings Playbook.” De Niro’s comedic chops, however, are usually wasted on subpar scripts where his characters turn out to be one-dimensional and bland (“Adventures of Rocky & Bullwinkle,” “Showtime,” the “Meet the Parents” sequels, “The Family,” just to name a few). The same can be said of his recent foray into the comedy genre with “Dirty Grandpa,” an embarrassingly unfunny and mean-spirited project that could only be described as the cinematic equivalent of a kick to the groin.

In “Dirty Grandpa,” Zac Efron (“Neighbors”) stars as Jason Kelly, a young and uptight lawyer who is tricked into driving his grandfather Dick (De Niro) to Florida right after burying his wife, Jason’s grandmother. While Dick unconvincingly reminds audiences he loved her, he is ready to move on soon after she is put in the ground. The reason Dick is so adamant about going to Florida is because after 15 years of life without having sex, he wants to get laid. A lot.

That’s the basic premise of “Dirty Grandpa.” It’s a movie featuring a grandson unwillingly driving his grandfather around so he can find a Spring Break-ing college chick to ride him back to 1963. Of course, raunchy things happen along the way that might have been considered darkly humorous if there was some sort of direction to all the cruelty (date raping jokes, pedophilia jokes, swastika jokes, homophobic jokes, and about a thousand penis puns), but these one-off attempts to shock audiences are nothing more than lazy and superficial gags that hang out there like disgusting little dingleberries.

Aside from grandpa being horny, director Dan Mazer (“I Give It a Year”) and first-time screenwriter John Phillips try to add some unearned emotion into the film with a side story about Jason rethinking his marriage to an overbearing fiancée and falling in love with a girl from the past. There’s also a badly executed storyline about fathers and sons and how making amends with one another is important. Mazer and Phillips want it both ways. Sadly, “Dirty Grandpa” refuses to understand that with a comedy like this it’s impossible to wear your heart on your sleeve if it’s already covered in semen.