It originally appeared in the Italian film Sweden: Heaven and Hell 
The film which is made up of nine segments focuses on different aspects of sexuality in Sweden such as lesbian nightclubs, porn films, the swinging lifestyle of married couples and the sex education of teenagers. The film also examines drug addiction, alcoholism and suicides in Sweden.

"Mah Nà Mah Nà" is a popular song written by Piero Umiliani. It originally appeared in the Italian film Sweden: Heaven and Hell (Svezia, inferno e paradiso). It was a minor radio hit in the U.S. and in Britain, but became better known internationally for its use by The Muppets and on The Benny Hill Show.

"Mah Nà Mah Nà" first gained notoriety in English-speaking countries from its use in a recurring blackout sketch for the 1969-70 season of The Red Skelton Show first airing in October 1969.

Sesame Street producer Joan Ganz Cooney heard the track on the radio and decided both it and a shaggy puppeteer named Jim Henson would be perfect additions to the show. First performed by Jim Henson (Kermit et al.), Frank Oz (Fozzie Bear et al.) and Loretta Long (Susan) on the fourteenth episode of the long running children's show broadcast on November 27, 1969, the song entered the public consciousness of the latter half of Baby Boomer children. The following Sunday when Henson and His Muppets performed the song on the Ed Sullivan Show it became an instant classic. Seven years later the song would also be part of the premiere episode of The Muppet Show in 1976.

Starting in 1971, The Benny Hill Show — in its second incarnation now at Thames Television where it launched in 1969 in color — implemented "Mah Nà Mah Nà" as part of a comic background music medley that would run during their often filmed slapstick sketches. The medley became a Benny Hill Show tradition for the rest of its run.
 Henri Salvador, French singer, added words to the music in 1969, under  Mais non, mais non.

MuzikLover wrote:

The Different is small. This is a song from an italian Porno. And later accidently used by the Muppets.    

 It's a good piece of Music (history). Go to a room with People and sing 'Mahna Mahna' and somebody is replay with 'ba di didi'. Ever.