One thing I can’t stand is when teachers pick favorites. It’s always the same type of person. The student is extremely interested in the subject (or even majoring in it) and speak up in class a lot. It makes sense that the teacher would like this student the best, but to others who just want to learn get really annoyed at this teacher-student relationship.
In my opinion, there is a fine line between being a teacher and being a friend. It’s much like the parent/friend ratio. If you are more of a friend to a student, the student will think that they can get away with things or get a better grade just because of the friendship.
I can’t imagine how I would balance that ratio!