If you live in a binary world where experiences are either stupid or brilliant, with a firm dividing line in between, you have my condolences. You’ll never appreciate the sublime idiocy of “Bad Grandpa,” my contender for funniest movie of the year.

I didn’t say best comedy, because a better film might try to touch the heart or mind in ways that “Bad Grandpa” never attempts. But in terms of explosive, laugh-the-shingles-off the-theater-roof hilarity, I haven’t seen a movie this good in ages.

The setup is a clever hybrid of scripted story and the “Jackass” team’s improv-heavy, hidden-camera stunt comedy. Encrusted in old age makeup. Johnny Knoxville plays 86-year-old Irving Zisman. Recently widowed and randy as a rooster, the old coot finds himself saddled with having to deliver grandson Billy (deadpan, delightfully guileless Jackson Nicoll) to his father, a thousand miles away.

Their road trip is the excuse for a cavalcade of elaborately choreographed pranks on unsuspecting bystanders, with Irving as the instigator and Billy as his sidekick.

Upbeat, grinning and lewd, Grandpa puts the moves on the ladies at a bingo hall, gets his dangly bits entangled with a soda machine, and makes the boy his accomplice on a takedown of a little-miss beauty pageant. The film explores realms of anatomically explicit, politically incorrect, exuberantly dirty-minded comedy that are indefensible by any known standard of decency. And, also, hilarious.

The movie is scurrilous and scuzzy, but there’s dedicated craftsmanship behind it. The physical humor is explosive yet precise. There’s a version of the old motorized-bed-run-amok gag here. It takes that premise further than anything I’ve ever witnessed.

Knoxville’s naughty-pensioner riffs are endlessly inventive, and the tone is carefully controlled. The gags are never at the onlookers’ expense. It’s all about capturing their gobsmacked reactions to Knoxville and Nicoll’s shenanigans.

“Bad Grandpa” has the thrill of a dirty joke, brilliantly told. This film is emphatically not for everyone, but if it’s not for you, too bad.