“Trolling Ted Cruz” would have been the most successful YouTube video Zach Etkind has ever made. Since 2012, the 28-year-old entrepreneur has been uploading jokey stunt videos to his channel, “Donnie Does,” in the hopes of achieving viral fame.

A handful of them have done pretty well: His top video, in which he pretends to be Roger Federer in the streets of Shanghai, has been viewed almost half a million times. But “Trolling Ted Cruz” was the real deal, some of Etkind’s best work. He made a sign that juxtaposed Cruz’s face with Brian Baumgartner’s — you might know him as Kevin from “The Office.” He drove 30 minutes southeast of Clemson, S.C. — where he currently lives — to a Cruz rally in Anderson. Then, while Cruz praised the great state of South Carolina, Etkind held up the sign and demanded to know whether Cruz and Baumgartner were the same person.

As he hoped for, the video went massively viral, earning more than 4 million views and a tweet from the viral kingmaker Buzzfeed.

https://twitter.com/BuzzFeed/status/703065633873743872

The only problem is that no one was sharing Etkind’s version. Someone had Vined a clip of his video, and everyone — including Buzzfeed — was sharing that.

“This Vine was stolen, shared by @buzzfeed, and now has been viewed almost 4 million times with zero credit given,” Etkind complained on Facebook. “I spent $18 dollars on that sign and almost got murdered by Secret Service and this is the thanks I get?!”

In a message to The Post, Etkind added that his lost ad revenue potentially totaled “a couple thousand” dollars. The person who pirated the video, meanwhile, is reeling in views and new followers.

YouTube creators call this freebooting: the practice of downloading and then re-uploading original videos without seeking permission from, or even crediting, their copyright holder. Since Facebook began doubling down on its video offerings last year, it’s become infamous over the issue; but networks like Vine and Instagram, as well as aggregators like World Star, also have a serious problem with freebooting.

In fact, one of the only other hits Etkind has had — a stunt called “Donny Does Pacquiao,” in which he snuck from nosebleed to ringside seats during a major match in southeast China — was subsequently stolen by World Star. Their version got 1.1 million views; Etkind’s got less than 300,000. Attempts to get the copy taken down were met with silence. Now, Etkind’s facing the same problem with Buzzfeed, which hasn’t responded to his tweet seeking credit for the video.

“I’ve definitely learned you can’t expect people to take the time to do their due diligence on where a video comes from,” Etkind said. “I don’t think its malicious, its just that they don’t care enough.” He’s going to start putting watermarks on all of his stuff.

The kid who stole it, meanwhile? He’s reveling in his ill-gotten fame.