Story highlights New Zealand's PM was involved in a radio station joke which referred to prison rape

His participation drew criticism and sparked a petition against him

He has made a series of questionable appearances on radio shows

(CNN) New Zealand Prime Minister John Key has been criticized for participating in a radio show stunt in which the hosts appeared to make light of prison rape.

During an appearance on New Zealand radio station The Rock on Wednesday, Key played along with a request from the radio hosts to get inside a cage in the studio.

Once in the cage, host Tom Furniss dropped a bar of soap and asked Key to pick it up, as those present howled in laughter.

Key complied, and Furniss told him: "You've got a pretty little mouth, Prime Minister."

"Dropping the soap" is a reference to prison rape. And Furniss' line references one in the film "Deliverance," in which a man is raped by two other men.