My vote for the most meta of all meta movie moments is in the otherwise forgettable 1963 Jimmy Stewart comedy Take Her She’s Mine. The film is a comedy that isn’t all the funny, and it did not succeed at the box office.
But it has one transcendently meta moment. During a wild chase scene on a cruise ship, while Jimmy Stewart’s character is trying to avoid being seen, he suddenly finds himself being chased by a group of Japanese men with cameras.
They are all excitedly shouting “Jimmy Stewart! Jimmy Stewart!” and chasing him around the ship. Unlike everyone else in the movie, they are somehow able to see him not as the fictional character he is playing, but as his real world self.
I can’t think of a single scene in any other movie that smashes the fourth wall with such a shameless sense of triumph.