Guess What Movie This Was?

Movies have been rated in the United States since 1968, and as I understand it the "PG" rating is supposed to mean (among other things) that the film contains no profanity other than "mild" swearing.

But there was one occasion (i.e. only one that I know of) when a movie studio committed an outrageous violation of the rating code and got clean away with it –– in 1976. The Internet Movie Data Base has a supposedly complete listing of the film's "profanity" content, which includes hell, damn, bitch and b*****d, as well as the S–word, and even "nigger" –– but there's no mention of the F–word, which if present would probably have required an "R" rating.

But in fact, the film actually contained what the censors considered the most profane word of all, the word "mother–....er" –– I heard it myself –– and yet it got a "PG" rating, which presumably can only mean that the rating board failed to notice that F–word occurrence. I can well believe that they did, because it was done so casually that most of the audience probably wouldn't even notice it. It happened in a scene with many people talking at once; the word was only heard softly, buried in a hum of voices, and the actor wasn't close to the camera when he said it. In fact, it was a "family" movie intended mainly for children, and the actor who said the word was only about 14 or 15 himself.

So what could easily have been a scandal becomes, instead, just a trivia question: What movie it was it?