In my first teaching job in a certain ex-soviet country, I was assigned to teach in the showcase class next to the office reception area. It was the showcase because it was slightly better equipped than the other classrooms in other parts of the building. the chairs were newer the light was better and it had the only white board in the whole school.

I made two main mistakes with that first class. The first mistake was telling the students that they were my first class. There was a stampede at the end of the first lesson with all of the students demanding to be switched to another class. The school administration, acting with the zeal only possible from those newly converted to the dogma of "the customer is always right," promptly emptied my group; only to have it reassembled a week later when the Director of Studies got back from holiday.

The second mistake was my "Oliver Twist"-like request for "more, please." More whiteboard pens, that is. More pens were duly proffered but only after surrender of the used ones.
The next day, I walked into class and the whiteboard had been replaced with a chalk board!