It’s not really a movie. It’s Johnny Knoxville, 42, and his Jackass crew faking out real people into believing he’s 86-year-old Irving Zisman, an old fart bag traveling cross-country to deliver his eight-year-old grandson, Billy (the up-for-anything Jackson Nicoll), to his father. Mom’s in jail for being a crack whore. Even when his balls are hanging out, Grandpa means well. Is Knoxville going soft on us? Nah. Bad Grandpa is still the fucked-up family movie of choice, especially if your family has done jail time. Knoxville remains an indestructible comic anarchist. But it’s disconcerting to see the Jackass team of Knoxville, director Jeff Tremaine and producer Spike Jonze collaborate on a script that has a beginning, middle and end. Don’t worry too much. Everything devolves into a series of hit-and-miss gags as Grandpa and Billy bust into a wedding, a funeral, a male strip joint and a child beauty pageant. Billy in drag grinds it out to “Cherry Pie.” In Borat style, hidden cameras catch real people reeling in horror. Hard to believe. Since MTV spawned the Jackass series in 2000, followed by multiple movies of scary stunts and scarier self-abuse, the shock value has worn off. The Kardashians have taken reality to a place no one wants to be. Knoxville keeps on keeping on. But if you’ve seen one old guy shit himself, you’ve seen them all.