Chi Soo having a melodramatic breakdown in the garage (in episode two) when his father takes the tyres off his car so he wouldn't drive it to school.
Chi Soo has another melodramatic breakdown in class in the fourth episode when he finds out Eun Bi won't take up the offer to get her job back, after she quits. After he runs out on the edge of tears, all the students look back to the teacher who continues teaching without a pause.
That misunderstanding with the neighbors thinking Eun Bi was in some sort of polygamous relationship. The boys certainly weren't helping matters either.