大姨妈大姨父喊你回家吃饭
[dà yí mā dà yí fù hăn nĭ huí jiā chī fàn]
"Your period (colloquially aunties) are calling you home for dinner" humorously indicates menstruation is happening. In China, "大姨妈", meaning an elder relative (like Aunt), is a euphemistic slang term used for women's menstrual period.