The film that is generally considered in wider critical world to be the best film ever made (although it is absent from Mark Kermode's All Time Top 10 Best Films Evs), and so often features as a comparison standard - eg "it's dull and bit poo but against The Reef, Charlotte's Web is Citizen Kane" or some such.
In August 2016, Citizen Kane itself was a potential TV Movie of the Week, with one listener suggestion Mark would recommend it on the grounds that "compared to everything else, it is Citizen Kane."
The fog in the movie, however, is disappointing, so when it came to the question of "what is the Citizen Kane of movie fog", Citizen Kane itself did not qualify.
Citizen Kane was famously overlooked by the Oscars and failed to find that much of an audience on release, two things that have bothered critics ever since. As Mark puts it, "compare the box office of Titanic and Citizen Kane and lose the will to live, frankly."