The Nelk Boys are being dragged to court over a YouTube prank video gone wrong -- the marijuana delivery driver they tried to trick is flipping the script on them with a very real lawsuit.

According to docs obtained by TMZ, a man named Nicholas Aliff claims he's the weed delivery guy in the YouTube stars' fake meth lab prank. In the video, he wasn't happy about being pranked and threatened to sue ... and now it looks like he's following through.

Aliff claims the Nelk Boys ordered weed and he ended up delivering the goods to a warehouse near Los Angeles, where the YouTube pranksters had set up a fake meth lab and hired an actor to play a cop who starts to make a drug bust before ultimately accepting a bribe.

The guy says he thought the actor was a real police officer, and he had no idea he was being pranked until after the fact, when the Nelk Boys told him it was all a joke. He says he reasonably became irate over the prank and started yelling at the guys, when their security grabbed him from behind and put him in a chokehold ... causing what he claims are severe physical and emotional injuries.

Aliff says the Nelk Boys lured him -- like a lamb to slaughter -- into their fake meth lab with the intention of frightening him and capturing his shocked reaction on camera. He says it felt so real, he thought he might get shot by the fake cop.

He's suing for assault and battery, false imprisonment, and infliction of emotional distress ... and going after the Nelk Boys for damages.

We reached out to the Nelk Boys ... so far no word back.

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