Calling a teacher's bluff

Last week a teacher in my daughters' school tried a bluff. She told the class that if anyone doesn't want to be there, she can walk out, and she would have no hard feelings. Obviously, she believed that people would be too embarrassed to take up that supposed offer. But one girl was not at all inhibited. She got up to go. The teacher tried to give her pause by amending the offer with an additional condition requiring a talk with the principal. The girl still went. Surprise, surprise, after the fact, the teacher admitted that she did have hard feelings about the girl leaving and would be calling her parents.

Moral of the story: Don't take a position that only work if no one calls your bluff.
Note: it was not my daughter who walked out. She's not the type to do it.