IN BAD GRANDPA, Jackass mastermind Johnny Knoxville dresses up like an old man and does things that old dudes aren't supposed to do, like perv on ladies and try to have sex with vending machines. And he's got a kid with him, and the kid does stuff that kids aren't supposed to do, like drink beer and say words like "asshole." And they do those things in front of unsuspecting passersby, who are horrified and amused and concerned, and some of it is funny and some of it is not. A fake penis is involved. A couple times.
Weirdly, Bad Grandpa crams these pranks into a narrative framework that's maintained throughout the film: Little Billy's mother is in jail, see, so Grandpa is delivering him to his deadbeat dad by way of a cross-country road trip. Billy and Grandpa never break character, even when it's just the two of them, yet most of the film's humor is derived from the pranks they play on unsuspecting bystanders, which the audience understands to be guerilla stunts that were actually performed.
The combination of fictionalized narrative with real-world hijinks is interesting on paper, but in practice it just feels like neither Knoxville nor the filmmakers—including director Jeff Tremaine and cowriter Spike Jonze—are really committed to their shtick. Am I overthinking a Jackass movie? Definitely. Is it because I was sorta bored during the Jackass movie? Yup. Some scenes are pure gold—whoever thought to have little Billy dress up like a girl and do a pole-dancing routine at a kids' beauty pageant is a goddamn genius (and Billy, played by Jackson Nicoll, is a charming, chubby little dancing bear of a kid). But a surprising amount of Bad Grandpa is just ho-hum. It isn't bad, exactly, but there's the thing: Johnny Knoxville is kind of old. His actual penis probably doesn't look so hot. And Bad Grandpa just seems a little tired.