Between gags, ‘Grandpa’ lacks ‘Jackass’-level humor

Strip the danger out of “Borat” and the injuries out of “Jackass” and you’ve got a bead on “Bad Grandpa,” a fitfully funny, semi-scripted “Jackass” outing built around elaborately staged pranks played on the unsuspecting.

Johnny Knoxville dons old-age makeup and becomes Irving Zisman, whom we meet at his wife’s doctor’s office.

“I thought she’d NEVER die.”

Innocent bystanders give him a look.

At the funeral, a hired black church choir freaks out – a bit – at Irving’s tasteless eulogy, and the mayhem with his crackhead daughter (Georgina Cates) that dumps the casket over in front of everybody.

A running gag in the movie: black people’s nervousness around a corpse. Another running gag: Irving’s racially tinged wisecracks to Hispanic store clerks, black cashiers and strip club fans, and a fetching Asian woman his 8-year-old “grandson” (Jackson Nicoll) befriends somewhere around Nashville.

The crackhead daughter’s dumped the kid on Grandpa. After a very public Skype Internet cafe rant with the kid’s no-good pothead dad (complete with bong hits) to rattle the patrons, we’re off on a bad grandparenting trek from Nebraska to North Carolina, complete with flatulence gags, sagging body parts, bad driving and a demonstration of extreme shoplifting.

There are explosive laughs in these stunts – grandpa sucker-punched by an airbag, hurled through a store window by a cheap kids’ ride set up out front. Most of this stuff you’ve seen in the very funny TV ads.

And the kid (Nicoll was in “Fun Size”) is flat-out hilarious, a natural “Jackass” in training.

The scripted interludes aren’t funny at all. The gags are more embarrassing than anything else. Take away that element of danger, that this irate restaurant or store owner may go off on Knoxville or that biker gang will flatten him, and “Bad Grandpa” loses some of that “Borat” appeal. Limit the stunts to a few rubberized genital gags and you lose a lot of that “Oh-no-they-DIDN’T!” Jackass appeal.

But a male stripper revue goes terribly wrong and a couple of tumbles involving transporting Granny’s corpse (portrayed by … Spike Jonze?) raise a funny eyebrow. And there’s a big finish.

As “Jackass” japes go, though, “Bad Grandpa” was better in concept and in its short, punchy TV commercials than it is as a feature.