Jackass isn't known for its character work, but some of its pranks and stunts have involved Johnny Knoxville and Spike Jonze dressing up in old-people drag for purposes of mischief. Apparently Bad Grandpa shot some scenes with Jonze (who also produced and cowrote the film) in his old-lady garb, along with Catherine Keener (!), but they were cut for time, leaving old Irving Zisman (Knoxville) immediately widowed, and giddy over his newfound freedom. But soon Irving is saddled with Billy (Jackson Nicoll), his eight-year-old grandson, and tasked with bringing him across the country to stay with his degenerate father. The pair bond over their wacky adventures, etc.
It sounds like typical raunchy comedy stuff, only the big set pieces, along with plenty of small set pieces, are filmed Jackass-style—as hidden-camera pranks on unsuspecting civilians. To some extent, this challenges typical comedic grammar: where a fully fictional comedy might have inserted cheesy reaction shots, Bad Grandpa offers real-life reactions to Irving hitting on women, trying to mail his grandson away, or shoplifting from a grocery store, running the gamut from open-mouthed horror to anger to quiet mortification. Knoxville, Jonze, and their director/collaborator Jeff Tremaine disguise the bad behavior of so many hard-R comedies as actual behavior, and in doing so—intentionally or not—call attention to the phoniness of the subgenre.
That's not to say Jackass: Bad Grandpa is devoid of phoniness itself. Zisman, as a character, modulates (depending on the scene) from full-on inappropriateness to straight talk, an old man who knows best. But while the occasional semi-scripted banter between Knoxville and Nicoll is gentle by Jackass standards—Nicoll, of the year-ago Nickelodeon bomb Fun Size, has an unaffected weirdo sweetness—it doesn't earn its feints at sweetness. Knoxville, as engaging as he is, only goes latex-deep in imagining Zisman; he's not as ingrained as Sacha Baron Cohen's Borat or Bruno. The sketches actually string together a bit better than Cohen's movies (even the full-fiction The Dictator, funny as it often was, was weirdly careless), but Bad Grandpa also lacks Cohen's satirical edge, maybe because Zisman secretly represents a vision of Knoxville himself as an old man: crankier, but still out for some mischief. In the end, that's all Bad Grandpa really is, and some of the best moments, including a climactic kid beauty-pageant, has been spoiled to death by trailers. But if it sticks around in theaters past its quick-kill opening weekend bonanza, it might make a nice comic chaser to Nebraska in a couple of weeks.