The singer makes the bizarre claim in his upcoming memoir, "Then It Fell Apart." In it, Moby details his alleged prank on Trump as well as his past flings with actresses Natalie Portman and Christina Ricci.
In an excerpt published in The Times, Moby, whose real name is Richard Melville Hall, recounted a party he attended "mainly full of businessmen and real-estate developers."
He wrote that when he and his friends who had been drinking noticed Trump "standing a few yards away" from them, one pal suggested Moby "knob-touch" Trump which he explains is "when you take your penis out of your pants at a party and brush it up against someone."
"'Really?' I asked. 'Should I?'" Moby wrote in the excerpt. He described Trump as a "mid-level real-estate developer and tabloid-newspaper staple whose career had recently been resuscitated by a reality-TV show."
"'S—,' I said, realizing I now had to knob-touch Donald Trump," Moby said. "I drank a shot of vodka to brace myself, pulled my flaccid penis out of my pants, and casually walked past Trump, trying to brush the edge of his jacket with my penis. Luckily he didn’t seem to notice or even twitch."
Moby has been sober for 15 years. Trump has not addressed Moby's claims and a rep for the White House did not return Fox News' request for comment.
In the upcoming memoir, the "South Side" singer also writes about dating then-20-year-old actress Natalie Portman for "a few weeks" in 2001. Moby was 33 at the time.
"I was a bald binge drinker and Natalie Portman was a beautiful movie star. But here she was in my dressing room, flirting with me," he writes in the book according to an excerpt in Entertainment Weekly.
The singer said he "tried to be Natalie's boyfriend" but was "relieved" when she called to tell him she had met someone else because he'd "never have to tell her how damaged I was."
Moby also claims to have had a fling with actress Christina Ricci in 2000 when she was 20.
He said he invited the "Casper" Star to his hotel room after performing at the Greek Theater in Los Angeles.
"I put my glass down and kissed Christina," he writes according to the Daily Mail. "I was with a smart, beautiful movie star and closing the book on the greatest 18 months of my life."
Reps for Portman and Ricci did not immediately return Fox News' requests for comment.