When reading Pnin last night for the first time in some twenty years I was struck by the similarity of Nabokov's description of Professor Blorenge to Clarkson Crane's description of a Berkeley academic in his forgotten 1946 novel Mother and Son. In section II of Chapter 6 Nabokov writes of Blorenge: "Two interesting characteristics distinguished Leonard Blorenge, Chairman of French Literature and Language; he disliked literature and he had no French."

A few years before this appeared Crane had written at the beginning of Chapter 3: "Gerald Stanley, who had taught French Literature for twenty-five years, had two ruling passions: hatred of literature and hatred of France."

Three hypotheses spring to mind: independent invention (unlikely); direct borrowing from the novel (possible, no evidence, but then we don't have it for much of what VN read: although could CC have been at the 1947 Utah writers' festival?)); or indirect borrowing, if the phrase was quoted in a review, say, or otherwise grew meme-oid legs. Wallace Stegner was another Bay Area academic and writer at the Utah conference, and hit it off with VN, and so could have been a possible conduit. Is Mother and Son a campus novel? Might VN have looked it up (perhaps at a Stegner prompting) as "research," if that were the case?

first and best The Western Shore (1925) is a campus novel, but an unusually lyrical and perceptive one. His second novel Mother and Son (1946) is set in Berkeley. Some of its better moments revolve around the university and its denizens, but I don't think the term "campus novel" well describes it. I have nothing to add to your plausible speculation as to Utah and Stegner and see that Mother and Son was widely (if none too favorably) reviewed in places like the New Yorker, the Masses, Kirkus, and the Saturday Review. (None of these quote the passage in question.)