On Monday's episode of Dax Shepard's "Armchair Expert," Kevin revealed this whole experience went down during his stage manager days at L.A.'s Raleigh Studios back in the '80s, while he was still searching for his big break as an actor.

Kevin recounted how a team of electricians arrived to rewire a stage at the studios for a higher-budget project, and he pitched in to help during the 3-week-long job.

But things took a turn when the workers led him to the grip room and laid out a line of coke, thanking him for all the hard work he put in. KC, who was trying to blend in, did what sounds like a total of 3 lines before realizing it wasn't his scene.

Rather than partaking further, he humorously requested compensation, joking to them, "Look, I’m trying to buy my first house. If you think what I'm doing's cool, I could use $20. I could take a twenty."

With that, Kevin was swiftly shown the door ... and to this day, he's got no regrets, explaining to Dax, "I saw myself excluded because I didn't want to do this. It was kind of lucky for me that I didn't like coke. There was nothing there for me."

Cleary, Kevin's career could've taken a much different turn had he continued using the drug -- but fortunately he didn't ... and went on to become one of the biggest actors in the modern era.

Instead, he solidified his movie star status by the end of the 80s with "The Untouchables" and "Field of Dreams" -- and by '91, he was a 2-time Oscar winner for "Dances with Wolves."