This 1967 movie contains a discreet fart joke where Hepburn sprays a deodorizer in the car to cover the smell. The joke is subtle by today's standards but can I assume it's the first fart reference in a mainstream movie?
shareThere's a scene in Two For The Road in which Joanna sprays Mark with a shower attachment (while he's taking a bath), but she never sprays deodorizer in any of the cars. That's Howard Maxwell Manchester's obsession; he sprays bug killer (twice) when he spots flying insects, and he sprays disinfectant (twice) in outdoor scenes involving Ruthie and her portable "john." But that's it.
Major studios wouldn't delve into the kind of humor you're referring to until Blazing Saddles.
The earliest fart joke I've seen in a movie is in Ozu's Good Morning. It has a recurring gag in which the two little boys eat pumice stone because they think it helps them fart better.
http://www.imdb.com/title/tt0053134/
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