The former "The Biggest Loser" star said she expected to be "gay homies" with Cohen, but instead he was "extremely rude, condescending and unprofessional" during their first meeting.
Michaels told the publication that she was "exhausted" while filming "Watch What Happens Live," as she was recovering from stomach flu at the time. The personal trainer said that after doing press all day and Cohen's show, the Bravo star brought out a shotski, which includes multiple shot glasses on top of a downhill ski.
"So he was explaining [the shotski] to me," Michaels recalled. "And I was a little bit out of it and I nodded like, 'Yeah I got it. So you drink the shot or whatever. He turns around again over his shoulder and looks at me and goes, 'Do you understand?'"
"And this was before the show started," she continued. "And it's live! So you can't leave ... At the end of it, I was like, 'I gotta tell you, that was a truly hideous experience. Like in all the years I've been doing this, nothing like this has ever happened.'"
Cohen recently slammed Michaels, who referred to their beef as a "weird little pissing match," on "WWHL," too.
"Tonight's 'Jackhole of the Day' goes to Jillian Michaels, who slammed the keto diet as an awful diet," he said earlier this month. "Don't feel bad, keto diet. A lot of people think Jillian Michaels is a bad idea."
In an US Weekly exclusive sneak peek at audio from the "Skimm'd From the Couch" podcast, Michaels clapped back and called Cohen an "asshole."
"Andy Cohen is just not a nice guy. And I've said that for many years," she said. "I had a really crappy experience with him on his show ... He's, like, constantly looking for, like, a way to pick at me ... He doesn't do keto. He doesn't believe in keto. He's just an asshole."