少年不流氓发育不正常姑娘不龌龊发育不正常
[shăo nián bù liú máng fā yù bù zhèng cháng gū niáng bù wò chuò fā yù bù zhèng cháng]
It literally means if a young man isn't naughty then he's not developing right, similarly if a girl isn't dirty/impure (in nature) she too is not developing correctly, probably pointing at natural rebellion and changes during youth but should not be taken seriously or out of context due to cultural variations in understanding.