正儿八经小青年吊儿郎当小青年
[zhèng ér bā jīng xiăo qīng nián diào ér láng dāng xiăo qīng nián]
Combining contrasting attributes of being earnest ('正儿八经') versus carefree or nonchalant ('吊儿郎当'), both referring to young adults. This indicates the duality in one's personality, suggesting seriousness alongside lightheartedness or playfulness.