The best adjective I can think of to describe Jin Wang is insecure. He certainly isn't alone in this description; as adolescents, most of us are/were insecure at least some of the time. Jin has typical moments of good old American teenaged insecurity, like worrying about whether he smells bad during his date with Amelia and running to the bathroom to put soap on his arms. When he is so anxious about it that he even has to have Wei Chen ask Amelia if she enjoyed the date, we know it's bad.

Still, it's important to remember that a fair amount of Jin's insecurity comes from the fact that he is a Chinese American, in a very white part of the country. He is plagued by stereotypes, ignorance, and bullying that cause him to try to distance himself from his Chinese-ness. He refuses Wei Chen's friendship at first, due to Wei Chen's dorky, overly Chinese appearance (not realizing that Wei Chen is in a much better place, self-acceptance-wise). When he changes his hair to look like Greg's, or worse, when Greg tells him to back off Amelia, it's clear that his race and culture are playing a role in keeping him from feeling at ease with himself. 

Even when he actually turns into the white boy Danny, Jin is still threatened by his insecurities in the form of Chin Kee. It isn't until hie apologizes to Wei Chen and enjoys some Taiwanese pearl tea that he can be said to have moved past his insecurities and feel at peace with himself.