The self-assured face and elaborate gestures that appear when one is explaining a concept that the he/she may not actually know much about. Usually accompanied by a condescending, stern voice and used by people who are known to be well educated in some previously explained remote subject. Not necessarily a sign of wisdom or of factuality, but a vehicle by which to convince the listener of your opinion or false set of facts and to make you seem credible.
Don't use that flock face on me, Michael Roy. I know for a fact that you were never involved in competitive opera.