By simply bringing her name up in an interview, of course!
That's just what happened on Monday when the real estate mogul called in to the Roz Weston & Mocha radio show on KiSS 92.5 in Toronto.
"Rosie is a bully," Trump said. "Bullies are people that you have to meet head-on, and I met her head-on. A lot of people didn't, but she didn't get away with it."
"I predicted correctly that Rosie would never make it," he boasted. "I did say that and she never made it, so that was sort of good and I was very proud of that, frankly."
A rep tells E! News that O'Donnell is not available for comment. However, the former talk show host did retweet the following from a fan: "Trump's rant shows 'weak grasp on reality."