The veteran stuntmen are being taken to court by Michael Vicens-Segura, who says he was approached by them back in 2018 to see if they could use his jet ski for a project they were filming in Puerto Rico.

Vicens-Segura insists the guys wanted to use it for a 'Jackass'-y feat -- where 2 guys are in the water on jet skis, facing opposite directions ... and attached to one another by a bungee cord, to see who would get yanked off first as they sped off.

Essentially, it's a jet ski tug of war ... and Vicens-Segura says the 'Jackass' guys have done something similar in the past -- in their movie, no less. It was called the BMX Tug of War.

Now, per the lawsuit, filed by attorney John Phillips and obtained by TMZ, Vicens-Segura was asked to hold one of the jet skis steady in the water because of the waves that day ... which he says he did. He claims, as Steve-O and Chris hit the gas, Steve's bungee cord snapped off the harness attached to his back ... which he says then flung in his direction and popped him hard on the side of the head, resulting in a massive gash.

Vicens-Segura says he had to be helicoptered to a hospital for emergency surgery, and even needed to be placed in a medically induced coma because he had a fractured skull and brain bleeding, among other things.

After several medical procedures, Vicens-Segura claims he was left in bad shape as he recovered ... and also had some pretty gnarly scars. He claims he's lost his ability to work, to think straight ... and continues to experience pain, suffering and agony because of what happened to him.

Of course, he's blaming Steve-O, Chris and others for the whole thing ... suing them for negligence and moreover the alleged incident. He's asking the court for more than $12 million in damages.