The 16-year-old climate activist gained headlines after footage of her glaring at Mr Trump arriving at the UN summit went viral in September.
Thunberg made the latest remarks about the US president, who has previously claimed climate change is a hoax “invented by the Chinese”, during an interview on BBC Radio 4 where she was guest editing the Today programme.
She said: “Honestly, I don’t think I would have said anything because obviously, he’s not listening to scientists and experts, so why would he listen to me?
“So I probably wouldn’t have said anything – I wouldn’t have wasted my time.”
The remarks come weeks after Mr Trump launched an attack on the Swedish Nobel peace prize nominee for gaining the accolade of Time magazine’s person of the year.
“So ridiculous. Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend! Chill Greta, Chill!” the US president tweeted.
Thunberg responded to the world leader by changing her Twitter bio to mock him. She updated it so it said she was “a teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend”.
Brazil’s far-right president Jair Bolsonaro has also previously hit out at Thunberg. “It is staggering, the amount of coverage the press gives that brat,” he said.
Thunberg hit back at her detractors’ attacks on Radio 4 after being asked about them.
She said: “Those attacks are just funny because they obviously don’t mean anything”.
Thunberg added: “I guess of course it means something – they are terrified of young people bringing change which they don’t want – but that is just proof that we are actually doing something and that they see us as some kind of threat.”
The activist, who turns 17 on Friday, also came face to face with David Attenborough over Skype while guest editing the Today programme.
Thunberg said: “It’s an honour to meet you.”
The naturalist replied: “I’m very flattered that you should say that.”
Sir David applauded Thunberg when the show’s host, Mishal Husain, asked him about her accomplishments.
“She’s achieved things that many of us who’ve been working for it for 20-odd years have failed to achieve,” he said. “That is, you have aroused the world. I’m very grateful to you. We all are.”
Sir David has previously heaped praise on Thunberg’s “passion” for climate change activism.
“How dare you continue to look away, and come here saying that you are doing enough when the politics and solutions needed are still nowhere in sight,” Thunberg told the UN at a climate change summit in New York earlier in the year.
She continued: “You say you ‘hear’ us and that you understand the urgency. But no matter how sad and angry I am, I don’t want to believe that. Because if you fully understood the situation and still kept on failing to act, then you would be evil. And I refuse to believe that.”