Who doesn’t love a good hoax? The audacity, the cheekiness of the hoaxer, losing yourself in the question of whether or not you’d have the nerve to try “Inventing Anna,” to attempt becoming “The Phantom of the Open,” much less the confidence trickster of “Catch Me if You Can,” makes such stories irresistible.

What about a hoax where the stakes are much lower, so low as to seem “just the most bizarre thing,” making those victimized by it ask “What would POSSESS someone to do that?”

“My Old School” is about a 32 year-old Scotsman who enrolled at a just-elite-enough Glasgow private school, inventing an elaborate back story and lying on the fly to explain his look, his past, his unwillingness to produce a birth certificate.

When it all came out the press labeled him “The Peter Pan of Bearsden Academy.” But some of his less kind classmates were onto something when they taunted this early ’90s enrollee with the nickname of a recently-broadcast American TV series — “thirtysomething.”

The movie is one of those what’s real/what’s fake documentaries — Orson Welles invented the genre with “F for Fake,” half a century ago — a film that presented unique challenges that encouraged a unique solution.

The 32 year-old who called himself “Brandon Lee,” same as the then-recently-deceased martial arts and film star and son of Bruce Lee, agreed to be interviewed for the film, just not on camera. So the director talked the Scottish stage and screen star Alan Cumming to come in, master the guy’s lines and lip-synch the picture, every line “Brandon Lee” speaks acted-out by Cumming.

Filmmaker Jono McLeod got many classmates and a few surviving teachers to sit down for interviews. And for the flashbacks, he hired animators to recreate the early ’90s school and pop culture in the style of that early MTV hit “Daria.”

The resulting film is a fascinating mystery, a weird case study and an unalloyed delight.

Part of the joy of it is how amused the former students — who went on to become an actress, a mixed-martial arts fighter, a pharmacist, a chiropractor and so on — seem to be at having been fooled, and at how the snobby school was utterly buffaloed by this stunt.

There are any number of places this story could have turned sinister — a secretive, sketchy grown man mixing and mingling with high school kids, impressing their teachers, stealing their thunder and starring in the class musical (It sounds like Cumming sings the animated snippets of “South Pacific”).

The play required an on-stage kiss between “thirtysomething” and a 16-year-old classmate. “Icky.”

But the deeper we get into this documentary, the more we learn about this fellow’s motives, the more questions we — and the reconsidering classmates — have, and the more we and they have to chew on the unreliability of memory.

McLeod makes “My Old School” a nostalgic catalog of the pop culture of the day — “Brandon,” secretive and slow to socialize, making a few friends, driving them in his car (a CLUE) to see “Muriel’s Wedding,” passing on mixtapes not of Ace of Base, R.E.M., UB40, The Pet Shop Boys or Scotland’s own The Proclaimers, but of late ’70s-early-80s punk like Black Flag, television and Hüsker Dü.

Yeah, that another clue, the now-adult kids realize.

And then there’s this man-among-kids influence on school culture and social life, a delightful turn that starts with having somebody around who “knew how to mix cocktails,” but who also helped more than one student with his studies and brought social outcasts into a new social orbit via “Brandon Lee’s” approval.

The real Lee’s story has bits of pathos and misdirected energy, but also cunning and entitlement. If his classmates, interviewed in a classroom at old school desks, can’t quite form an opinion of him, what chance do we have?

The film’s third act turn towards the light side plays with those faulty memories and takes on a “28-Up” tone as we see how the kids have turned out, despite or perhaps because of this disruption of their last year of childhood by this stranger in their midst and the media circus that erupted when it all came out.

I don’t know if there’ll be a feature film on this subject (I seem to recall this project starting life along those lines), but it’s a natural — the dark parts of “Catch Me if You Can” married to the lark of it all of “Phantom of the Open.”

Perhaps Alan Cumming can play the earnest but self-important head master. Be a shame to leave him out of it.

Rating: unrated, some profanity

Cast: Alan Cumming, Juliet Cadzow, Dawn Steele, David Tattoo Dave McKinlay, with the voices of Lulu and Clare Grogan,

Credits: Scripted and directed by Jono McLeod. A (July 22) Magnolia release.

Running time: 1:44