The 82-year-old actress and political activist recalled a run-in with Kardashian during Thursday's episode of Watch What Happens Live.
Fonda shared the story while playing a game of "Have! You! Met Them?!" where she answered whether she's met different celebrities. She said she met Kardashian at the Clive Davis pre-Grammy party.
"I was kneeling on the floor talking to Gladys Knight, because Georgia's my second home and Gladys lives in Georgia. I turned around to get up and right in my face was this shape," Fonda said, miming an exaggerated hourglass shape.
"I thought, 'That is the most amazing behind I have ever seen,' and of course, it was Kim Kardashian," she added. "And so I told her, 'I've just been staring at your behind, and it's beautiful.' And she was very sweet."
Fonda said she and Kardashian have since chatted while getting their nails done at the same salon.
"We used to go to the same manicurist, and we would chat from her seat to my seat. She's very friendly; just one of the gals," she said.
"When I was making ... On Golden Pond up in New Hampshire, he came and lived with me for about a week in the same home," the actress said. "He slept on a mattress that he pulled out on the floor of the living room; I slept in a loft upstairs."
"I found him very touching, a very interesting character," she added. "I knew him pretty well. I went to his house a lot; he came over to my house a lot."
Fonda said she and Jackson weren't close in the later years of the singer's life, but did say she once went skinny dipping with the star.
"Put that in your pipe and smoke it," she said.
Fonda urged people to take action against climate change during an interview with Late Night with Seth Meyers earlier this month. She shared her belief in civil disobedience and its ability to change history.