Dan Mazer, the man credited with directing “Dirty Grandpa,” isn’t a filmmaker.
Sure, he has a few writing and producing credits mostly associated with Sasha Baron Cohen, but to call him a filmmaker would imply he tells stories, and that would imply “Dirty Grandpa” is a story. 
Instead, “Dirty Grandpa” is a hodgepodge of fart jokes, racism, homophobia and sexuality so retrograde and tasteless that “dirty” isn’t the right word. “Pointless” Grandpa. Abysmal Grandpa. Either would be more appropriate.
When it’s not offensive, it’s cliche, and when it’s not cliche, it’s boring. It’s only 102 minutes, but you’ll swear it was longer. 
The “plot” revolves around Jason  — played by Zac Efron — driving his grandpa, Dick  — played by Robert De Niro — to the beach for some spring break good times. You see, Dick’s wife of 40 years recently died, and it was her wish that he get back in the game. Meanwhile, Jason is weeks away from marriage and a steady lawyer position, and wants none of his grandpa’s shenanigans. 
What happens next is a myriad of outdated tropes and unfunny gags that do nothing to buoy the paper-thin plot. The sex-quest is fueled with expletives and innuendo, but none of it is funny or interesting in the slightest. It’s gross for the sake of being gross, and its attempts at humor don’t work. The biggest laugh in my screening came from an image of De Niro’s stunt genitals. I’m not really sure that counts as a joke. 
Look, this doesn’t need to be a long review. “Dirty Grandpa” is not a good movie. It’s hardly a movie at all. It has some of the trappings, sure — there’s music, credits and even actors — but it lacks a soul, a purpose, or anything worth talking about. 
So please, don’t go see “Dirty Grandpa.” The last thing we need is people thinking we as viewers want more of this garbage.