Johnny Knoxville is up to no good as an grumpy octogenarian in Jackass Presents: Bad Grandpa

Beware of the old dog with new tricks in the fourth film of the Jackass franchise, a familiar combo of the lewd, crude and disarmingly imaginative

Rating: Two and a half stars

Director: Jeff Tremaine (Jackass: The Movie)

Starring: Johnny Knoxville, Jackson Nicoll

That "Jackass Presents" tag frontloaded to the title of Bad Grandpa is either a call to arms or a cinematic health warning.

All depends on where you stand on all things Jackass. You should know by now whether you've had your fill of the franchise's relentless stunt-prankery.

If you haven't, well, Bad Grandpa's familiar combo of the lewd, the crude and the (sometimes) disarmingly imaginative will deliver upon expectations.

Johnny Knoxville plays - no, make that poses as - a newly-widowed 86-year-old named Irving Zisman.

As this movie is all about punking the real world with carefully constructed shonky shenanigans, it isn't long before this self-styled Bad Grandpa is up to no good.

A bizarre sequence in a funeral home - where Irv's late wife Ellie (Catherine Keener) is bundled out of her casket on a number of occasions - lowers the bar for the high-jinks to follow.

Soon enough, Irv is out on the open road, with his eight-year-old grandson Billy (Jackson Nicoll) riding shotgun. The pair wander all over the American south on the lookout for fresh suckers to fool.

Irv likes a drink, loves the ladies, and lacks the caring skills to properly look after Billy for more than a few hours at a time.

Luckily, Billy is one of those kids who knows how to keep going when the going gets tough.

There's no other way of putting it: Bad Grandpa is a movie of bits that is sure to have its target audience in pieces by the close.

Set-piece sequences in a strip club, outside a department store and inside a biker bar are among the dubious highlights, as is the surprise storm-trooping of a children's beauty pageant.