“Jackass Presents: Bad Grandpa,” in which “Jackass” star Johnny Knoxville presents himself as a bad grandpa, contains shock-laugh jolts delivered with such brutality that no one's quality filter will protect them from bursting into helpless, dumb giggles. This does not mean that “Bad Grandpa” is a good or even passable movie — it is one of those rare films that would be improved in just about every way if Knoxville and director Jeff Tremaine dumped every scintilla of plot and pathos off a bridge somewhere.
Knoxville's gift for demanding physical humor is worth high praise — he's like MTV's version of Buster Keaton or Harold Lloyd, except that those geniuses of the silent era never detonated a squib full of brown gravy from their backsides.
In “Bad Grandpa,” he plays Irving Zisman, an 80-something widowed codger looking forward to exploiting his recently acquired marital freedom for all it's worth. But then his prison-bound, crack-addicted daughter dumps her son on him in the middle of his wife's funeral, forcing Irving to take Billy (Jackson Nicoll of “Fun Size”) and his wife's dead body on a cross-country trip to North Carolina, where he will be raised by his criminal-minded, bong-smoking father.
The “Borat”-style hook is that all this fiction is being played out in the real world, where Irving and Billy's anti-social exploits can shock, amaze and stun all the yokels who cross their paths. But unlike “Borat,” which earned at least half its laughs from showing the inappropriate responses from people who were taken in by Sacha Baron Cohen's character, the real people in “Bad Grandpa” are not as engaged — they mostly gawk or shake their heads. It's like an extended and extremely ambitious “Candid Camera” gag with some unfortunate nods to “Weekend at Bernie's.”