This one is a little different. On the first week of some college introductory economics class, the teacher was basically just reading from the textbook we all had, some historical figure who was a member of the "Council Of Seven" or something like that, when a student raised her hand - "Ma'am, what was the Council Of Seven?" - the teacher paused, and said - "Can you bring it tomorrow, as assignment?" - and actually giggled. This was in the 90s, pre-internet, looking up something like that was not a trivial task.

The teacher might have thought she was being cute and/or deflected her own shortcomings, but the actual effect was that we immediately lost all respect and trust for her, no one ever raised a hand again in her class, we all immediately went into rote robot mode for the rest of the semester, disengaged on a gut level.