当大姨妈遇上了大姨夫
[dāng dà yí mā yù shàng le dà yí fū]
The menstrual period encountering the husband's paternal aunt, is a joke phrase. Used when women have menstruation during sex. The phrase vividly describes the inconvenience caused by a woman having her period during intimate moments with a relative, but in a humorous way using Chinese kinship.