pretentious know-it-all; person who fakes expertise
Describes someone who acts like an expert but has only shallow knowledge. Often used critically or humorously. The literal meaning is 'vinegared tofu', but the idiomatic sense is the only modern usage.
He always uses difficult words, but he's actually just a pretentious know-it-all.
That know-it-all's talk isn't worth listening to.
From the comic story 酢豆腐, in which a pretentious young man presents spoiled tofu as a delicacy to avoid admitting his ignorance. The title consequently became a term for a person who feigns expertise.