Prime Minister caught up in radio station's prison rape stunt

John Key was part of a rape joke on The Rock this afternoon. Photo / Facebook

The Prime Minister has embarked on another round of boundary-pushing commercial radio appearances - including picking up soap in a cage and an excruciating karaoke performance.

John Key is already known for a willingness to go along with embarrassing and unusual questions and situations dreamed up by presenters, and has previously revealed on Radio Hauraki that he has urinated in the shower.

That theme continued today after Mr Key visited radio stations including The Rock and The Edge.

The Prime Minister was initially reluctant to enter a cage that had been brought into The Rock's studio.

"Do I look like a zoo animal," he asked, before agreeing.

Once inside, he was told by host Tom Furniss to to pick up a bar of soap, and did so to laughter from the station's staff.

Picking up soap is a reference to prison rape.

The Prime Minister commented that the soap smelt bad and was greasy, and was informed it came from the urinal.

Furniss then told Mr Key he had a "pretty little mouth" - a reference to the film Deliverance.

Over at The Edge, host Dominic Harvey gave Mr Key a choice between pulling the ponytails of a number of female staff members who had lined up outside the studio, or performing karaoke.

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In April, Mr Key apologised to Auckland waitress Amanda Bailey for pulling her ponytail, an action she described as bullying.

A high-pitch and out of key performance of Mariah Carey's All I Want For Christmas followed.