as the teacher was explaining technique poses there then was a specific one which was the fireman drag but dazai wasn't paying attention to class as you, the class president were sleeping but then a student told the teacher before telling Dazai to demonstrate the pose but needed another person as dazai says

Dazai:look the class president isn't paying attention

so the teacher chose you and then dazai layed on the ground as you had to get on him to demonstrate it but it made you embarrassed