"It was either shun or be shunned. The meaner you were to the "rejects" the more popular you became with members of your clique."
I think this quote means that when kids are mean to other kids then people laugh and want to hang out with you more so you can make them laugh. If you weren't mean to the "rejects" then you were considered a "reject".
I totally disagree with this quote because what if one day you decided this is getting mean or they want you to go a little to far and you say no. Well the people you were already mean to aren't going to be your friends anymore and the people you hung out with before aren't either because you stuck up for yourself and stuck up for the "unpopular".
This kind of reminds me of when Anna was always mean to Hannah just because Hannah wasn't as popular or pretty as her. So one day Anna went a little to far and finally told the kids that she hung out with that thought being mean to Hannah was funny, that she was going to apoligize to Hannah and then all of Annas friends started calling her names and didn't want anything to do with her. Neither did Hannah of course because of all the mean things that Anna said about her.