男生必须有大姨夫
[nán shēng bì xū yŏu dà yí fū]
The phrase humorously states, 'men need to have “Da Yifu”, which refers colloquially to menstruation-related cramps'. Here it humorously implies that men should experience menstrual cramps so they better understand female experiences. Note: Menstrual cramp is referred humorously to '大姨夫' in China.