滥情少女烂心少年
[làn qíng shăo nǚ làn xīn shăo nián]
This translates literally to 'A promiscuous/indiscriminate girl, a spoiled boy'. Both parts refer to people who are not emotionally stable. On one side it portrays someone involved superficially in romance (over-involved without seriousness), while on the other, it refers to immaturity in dealing with feelings.