Full disclosure: The title of this post is clickbait. I haven't actually invited students to flip me the bird this semester.
What I have done, however, is invite students to give me some kind of silent and subtle indication-- we agreed on a flick of their pen or a slighttly-raised finger-- whenever I use a word that they don't know or when I use a word they do know in an unfamiliar way.
Now, when I see one of these signals, I stop and explain the term. I do not call the questioner out. I do not explain the term to him or her directly. I do not resume the lecture or discussion until everyone in the room is crystal clear. This experiment has been unbelievably useful and, only a month into the semester, really surprising in several ways.