班主任的前世是容嬷嬷么
[bān zhŭ rèn de qián shì shì róng mā mā me]
A humorous play on characters from Chinese pop culture. '容嬷嬷' (Lady Rong) is a strict, sometimes mean nanny in a drama. This implies their homeroom teacher might have once been her, suggesting the teacher's strictness.