I'm paraphrasing slightly, but there's a moment in Jackass Presents: Bad Grandpa where Johnny Knoxville, in the role of senior citizen Irving Zisman, tells onscreen grandson Billy (Jackson Nicoll), "You can do pretty much anything you want; you just have to try." It's the American Dream in a nutshell, but I'm not sure the classical patriots who came up with that philosophy ever expected it would be used in defense of disrupting a stranger's wedding to snag some free cake in the chaos. Yet it captures the strange heart beneath the goofiness of the gag.
Bad Grandpa is undeniably funny in parts, just as porno movies with excessive amounts of plot occasionally give you a boner. And both are equally confused about what they want to be. Bad Grandpa began as a recurring segment in the Jackass movies, which were the hidden-camera prank equivalent to gonzo porn, with no story to get in the way of the endless money shots. In this film, however, there's a plot - in what is clearly an attempt to equal Sacha Baron Cohen's work as Borat and Bruno, Zisman and Billy actually follow a story, in which the kid is being taken cross-country to be with his dad after his mom has had to go to jail. Along the way, real unsuspecting people will encounter the duo and deal with their crazy hijinks.
Crucially, however, it lacks the faux-documentary gimmick that Baron Cohen's films utilized, resulting in awkward visual transitions between the grainy, low-light hidden-camera stuff and the perfectly lit insert/transition scenes that further the story. A more apt comparison, unfortunately, is The Crocodile Hunter: Collision Course, which awkwardly juxtaposed video footage of the late Steve Irwin mugging for the camera with wild animals, and an awkward spy plot shot on film.
Knoxville was apparently worried that an all-prank movie with just Zisman would become tedious, and added the story to give it some extra value, but it's hard to focus on said story when the transitions are so obvious, and you merely wind up wondering, for instance, how MTV Films enticed complete strangers to come to the funeral of somebody they didn't know. Knoxville and Nicoll do genuinely good work with their characters - bizarrely, it wouldn't be hard to make the case that Zisman is one of the most well-rounded portrayals of an old man onscreen in any major American film this year - yet you can't fully buy into their emotional arc when, at every opportunity, the movie rubs it in your face that this is that Jackass guy pranking people. An entirely conventional filmed comedy with this pair could have worked, and I suspect a gonzo, Jackass-style montage would have been decent as well. Putting the two together results in a final product that's only half as good.
That doesn't mean you won't laugh when Zisman picks a fight over a giant porcelain penguin, or sharts so hard on a diner wall that you may have to avert your eyes so as not to puke, or truly lets his nuts hang at an African-American male strip bar. What it does mean is you may wish you had a fast-forward or skip button to cut straight to the harder chuckles, past the aimless scenes of driving.