What sounds like a fun look at a particularly outre subculture turns out to be no laughing matter in “Tickled.” David Farrier and Dylan Reeve’s documentary traces the New Zealand duo’s investigation of an online tickling-video empire, behind which there lurks a monster of cyberbullying and litigiousness. An alarming cautionary tale about how easy it is in the Internet age to ruin people’s lives while hiding behind a cloak of anonymity, the pic boasts a humorously titillating entry hook that soon gives way to engrossing conspiracy-thriller-like content. It should attract healthy sales in various formats, particularly cable broadcast.

Farrier is an Auckland-based TV and radio reporter/personality who’s “made a career looking at the weird and bizarre side of life.” He assumed he’d found just more amusingly offbeat grist for the mill when he stumbled upon an online video offering substantial cash and all-expenses trips to Los Angeles for young athletes willing to participate on camera in the “sport” of “Competitive Endurance Tickling.”

But upon contacting these events’ producer, Jane O’Brien Media, for an interview, he was surprised to receive virulently homophobic responses (Farrier is an out gay man). This seemed ludicrous, since nothing could be more blatantly homoerotic than videos of mattress-bound youths being straddled and tickled all over by other handsome junior jocks. The long-distance insults rapidly took on a lawsuit-threatening nature. Now Farrier and his (straight) collaborator Reeve were intrigued enough to decide their inquiry might merit a whole documentary, despite (or because of) the intimidation tactics.

Traveling to the U.S., they discover only one among a hundred or more former tickling-video participants is willing to talk to them. Others (many underage) are too afraid of reprisals like those the sole exception has already experienced: When TJ objected to footage being disseminated beyond what he’d agreed to, he found himself the victim of a viciously public harassment and slander campaign that seriously impaired his hopes of a pro football career.

The filmmakers also dig up David Starr, a Hollywood fringe dweller and onetime casting agent for “Terri Tickle.” The latter was, like O’Brien, a highly elusive figure who’d run a remarkably similar operation starting in the mid-1990s, and whose activities ceased just about the same time O’Brien’s commenced. When Starr refused to continue procuring young men for reasons similar to TJ’s, he, too, was subjected to exhaustive, elaborate and vile efforts at public and private humiliation — not sparing even his elderly mother or the name of his deceased brother.

Eventually (amid an unending barrage of legal threats), the trail leads to a single, shadowy apparent perp with the inherited wealth to sustain this fetish habit on an international scale — and the maliciousness to deploy blackmail, false identities and more in protecting it. “Tickled” becomes a frightening illustration of how one bully with deep pockets and a mean streak can largely evade punishment, even detection, while wreaking havoc with far-less-privileged others.

On the flip side, we meet Florida entrepreneur Richard Ivey, who is cheerfully upfront about his own successful tickling website (“My Friends’ Feet”) and its advertised aim of providing “Gay Foot Fetish Heaven.” We also see him film a typical session with one consenting, hirsute twentysomething “hunk.” There is no question whatsoever that despite O’Brien’s preposterous claims, all this stuff is just (as Ivey puts it) “whips-and-chains bondage, dialed way down,” yet still clearly designed to arouse. The difference being that Ivey isn’t hiding his intentions, let alone exploiting (or threatening) his consensual participants.

While the filmmakers are often onscreen, “Tickled” is no vanity project — their presence is justified because the harassment they experience in pursuing the story becomes a big part of its narrative. The well-shot and tightly edited pic manages to maintain a sense of humor without belittling its subjects, and glimpses a somewhat gamey underworld without descending into a tabloid-style shocking expose.