班主任是容嬷失散的孩子
[bān zhŭ rèn shì róng mā shī sàn de hái zi]
This nickname combines 'class teacher' with 'Empress Dowager Rong', who appears in ancient palace dramas as a character that is often seen scolding people. It's used humorously to portray someone who nags a lot like the teacher or Empress Dowager Rong does.