The butter thing comes from the film
Last Tango in Paris and in the film it's a spontaneous act, not a methodically planned attempt to use butter for lubrication. I would think that, given a little while to ponder the situation without a raging hard-on and certain psycho-sexual hangups, even Marlon Brando might have opted for K-Y or its early 1970's equivalent. But sometimes things just get outta hand, ya know?
