The Forgetting Sarah Marshall star made an appearance on talk show The Project to promote his comedy tour Down Under, and he stunned the presenters by launching into a foul-mouthed rant about new leader Malcolm Turnbull.

"Why do you put really rich people in charge of your country who want to build a thing called a tax shield?" Russell declared. "Also... he's got money in the Cayman Islands but there's nothing wrong with it? Having your money in the Cayman Islands is like putting your d**k into custard. We all want to do it but there's no rational reason to do it. If your d**k's in a bowl of custard, you're doing it for a reason."

The comedian's language prompted one of the hosts to interrupt and remind him about the live broadcast, saying, "Just reminding you, we are live..."

However, the star avoided apologising and instead smiled and waved at the camera, saying, "Hello mum!"

Later in the show, the funnyman joked that he may need a lawyer because he "accused (the) Prime Minister of putting his d**k in custard."