It happened at her show on Friday in Vegas. He's in town because of the Academy of Country Music awards . . . and got the chance to see her in concert. They were hanging out backstage when she asked if he could dance.
The answer was no . . . but she invited him to join her on stage anyway. Apparently, she was planning to "fake humiliate" him during her song "Freakshow".
He said, quote, "I didn't know what I was going to have to do, so I get up there and they put me in these chains, a collar, and a leash, and made me get on all fours and crawl across the stage, while she was whipping me, with a whip. I was laughing so hard.
"My inner sixteen-year-old self was freaking out."