班主任是容嬷嬷派来的卧底
[bān zhŭ rèn shì róng mā mā pài lái de wò dĭ]
In Chinese pop culture, 皇阿玛和容嬷嬷 come from a popular period drama about imperial life where ‘Empress Rong嫫嬷’ is seen as cunning. Thus, 'The class teacher is an undercover spy sent by Empress Rong' humorously suggests the class advisor might secretly surveil students' behavior or activities—similarly watchful and stern—creating an amusing, light-hearted image of authority figures observing students closely, possibly even in less-than-favorable scenarios.