'Judy, Judy, Judy!'
In the Criterion DVD features, Stanley Donen describes how he got Cary Grant to say this. When they had finished the second-to-last scene in the taxi cab, Donen asked Grant to do him a favour. As we all know, Cary Grant never actually said "Judy, Judy, Judy" in any film role but Donen wanted him to do it with the camera running.
He complied but that bit of film was lost!