When someone dressed in slacks and a button down walks into your classroom on the first day of school and starts writing the course and his name on the chalkboard, it becomes evident that he is the professor.
Or is he?
He simply walked into the lecture hall and began introducing himself and the course, focusing on how strenuous the curriculum would be for most students. The students instantly quieted down and started taking notes.
Only when the real Mr. H entered was the prank exposed.