‘Bad Grandpa’ lives up to his name

If you liked the “Jackass” television series and its movie spinoffs, you’ll probably love “Jackass Presents Bad Grandpa.” Starring Johnny Knoxville, the chief perpetrator of many of the disgusting and/or painful-looking stunts featured in those reality shows and films, “Bad Grandpa” is a loose sequence of hidden-camera pranks centered on the outrageous antics of a fictional octogenarian. Some of them are quite funny, but only to the degree that you are able be amused by explosive diarrhea and the effects of age and gravity on certain parts of the male anatomy.

“Bad Grandpa” has only the most superficial of plots. Irving, a lecherous, foul-mouthed and wildly irresponsible old coot created by Knoxville during his television show, is driving his 8-year-old grandson, Billy (Jackson Nicoll), across the country. Knoxville’s old-age makeup looks strikingly real, and most of the people he encounters take him for exactly what he appears to be: an elderly idiot. In structure and concept, the film resembles the faux-documentary “Borat,” with the distinction that the cameras here are all hidden.

And that is where the film falls down and can’t get up. Unlike in Sacha Baron Cohen’s 2006 punking of Middle America, the reactions of the people who are fooled by Knoxville’s “Candid Camera”-style stunts just aren’t all that funny.

Yes, there are some hilarious setups. Irving hires unsuspecting movers to help him load his late wife’s corpse (co-producer Spike Jonze in drag) into the trunk of his car; Billy, also in drag, enters a child beauty pageant, performing a raunchy striptease to Warrant’s “Cherry Pie” before an audience of shocked parents; Irving soils himself flamboyantly in a diner. But most of the folks caught on camera seem stuck somewhere between bemusement and mild alarm. Only a grocery store owner who catches Irving and Billy shoplifting musters anything close to real outrage.