Like Ian, I cannot recall even one stupid comment from the two wonderful teachers I had in my youth. The converse wasn't true though, I was a mine of silly remarks, beats me what they ever saw in me.
During a masterclass:"If I can physically knock you over, you aren't playing with enough weight." To demonstrate, the teacher began to play and asked me to try to remove his hands from the keyboard as he played. Apparently some faculty heard him practicing on the pianos beforehand and noted his delicacy of touch similar to a jackhammer. They feared for the health of the instrument.
Not at all related to piano, but I had a music faculty associate imply that I only got into my elite college because I'm Latino, then proceed to ask me to help their child with Spanish homework...