Earlier I wrote that a scene from Kitten With a Whip (1964) was "one of the first references to Warner Brothers cartoons in a non-WB movie." I'd forgotten about the ending of the 1958 Paramount production The Geisha Boy:
Of course since Frank Tashlin wrote and directed this movie, you could argue that this is more of a Looney Tunes insider reference than anything else. But still, it might be the first time that Looney Tunes cartoons were referred to as a general cultural reference instead of Warner Brothers plugging itself (e.g. My Dream is Yours).
Jerry Lewis's delivery of the Porky Pig line isn't all that good, by the way. He doesn't seem to realize that he's not supposed to stutter on "folks."