Everyone's a critic, including the very teachers who are supposed to guide students along their path to success. When senior art critic Jerry Saltz asked artists to dish on their worst art advice from teachers, he got some incredible responses. He posed the question in a tweet, asking, "Artists: Did you ever have a bad art-school critique that really set you back, knocked you off your pins? What was it? Keep it short; don't exaggerate. Often, it can be the least thing. Have you ever made a “rev…