菇凉你姨妈巾掉了
[gū liáng nĭ yí mā jīn diào le]
This nickname is a humorous statement. In Mandarin, '姑娘'(Gu1niang2)—a respectful term addressed politely toward unmarried young ladies—was misused phonetically similar word here instead: 菇凉(Gu1liang2), plus a colloquial remark regarding female physiology (sanitary pad dropping), suggesting surprise or mischief.