Starring Johnny Knoxville and Jackson Nicoll. Rated 14A. Now playing

Bad Grandpa’s greatest trick isn’t convincing the world that Johnny Knoxville truly is a perpetually horny octogenarian named Irving Zisman. What’s impressive about this funny but wrong-on-so-many-levels cross-country odyssey is that it’s got a legitimately sweet heart. 

Get past the epically tasteless gags, and you’ve got a strangely touching tale of a boy bonding with his granddad. If that sounds icky, don’t worry—Zisman rogering the living shit out of a convenience-store pop machine compensates for the tender moments, especially when he gets his schlong caught in the coin slot.

Thanks to the magic of prosthetic makeup, Knoxville is unrecognizable as Zisman. Bad Grandpa has him hitting the road with his young grandson Billy (the smartly cast Jackson Nicoll, who makes everything seem cute, whether he’s getting beer-bombed on a park bench, or asking strangers to be his dad).

The film is a mashup of Borat, Little Miss Sunshine, and Candid Camera, the scripted moments showing grandpa and grandson bonding over farts, farts, and sharts serving as lead-ins to the money shots: secretly filmed real people reacting to stunts that are either bone-breakingly physical or well beyond the boundaries of acceptable behaviour in civilized societies.

There are plenty of morals to this story, which has some genuinely big comedic payoffs. One is that North Americans are fucking stupid (and not just the ones who find the Jackass crew funny). What kind of cretins help a confused senior citizen mail a kid cross-country in a cardboard box?

The bigger one is that old men are hilarious because they don’t care what anyone thinks of them. So if your grandfather has ever gone up to a young stranger on the street and announced “I’m too old to stir the gravy but I can still lick the spoon,” Bad Grandpa will make you happy you aren’t alone.