godan verb (-ru)
act like a know-it-all; pretend to be an expert
Used for someone who acts as if they are deeply knowledgeable or 'in the know', often with a negative or mocking tone. The verb is derived from 通 (つう, 'connoisseur') + がる (suffix meaning 'to act like').
彼はいつもワインに通がっていて、うんざりする。
He always acts like a wine connoisseur, and it's tiresome.
そんなに通がらなくてもいいじゃないか。
You don't have to act like such a know-it-all.