The 88-year-old actress hit out at the 90-year-old actor - who played Captain James T. Kirk in the "Star Trek" films and TV series - after he became the oldest person to go to space earlier this month.
"What a fool," she said on "The Jonathan Ross Show". "Who wants to do that? No, absolutely not! Did you see Bill Shatner? He was in the air and they were turning him upside down."
The actor ventured up into space with former Amazon CEO Jeffo Bezos as a part of the billionaire's Blue Origin project, which seeks to run commercial space flights.
The 11-minute flight made headlines all over the world, but Joan thinks it was irresponsible and damaging for the planet.
"Let's take care of this planet first before we start going off," she sighed.
By contrast, the Hollywood star previously admitted to loving his space experience.
He said shortly after returning to Earth, "Everybody in the world needs to do this. It was unbelievable."
"The Jonathan Ross Show" airs in the U.K. on Saturday (23Oct21) at 9.30pm BST on ITV and ITV Hub.
The actress starred as diva Alexis Colby from 1981 to 1989, and she's revealed that the former U.S. President did everything he could to join the cast.
She told The Jonathan Ross Show, "He pretended to be (taken with me) - I don't think he was."
"I was a great friend of (his ex-wife) Ivana's. Then he called up one of the producers from Dynasty and said, 'I want to be in Dynasty.' He said, 'I'm sorry we're all cast.' Trump said, 'But, I am Dynasty!' And he said, 'No you're not. We have all these other people.' "
"Trump said, 'Look, I'd be great to play one of Alexis's lovers.' He said, 'I think those parts - there was a few! - have been cast.' A few weeks later, (the producer) spread this story around Hollywood, he (Trump) denied it."
"Trump said, 'I would not want to be Joan Collins' lover on or off screen.' Which I thought was rather rude!"