Sure he did it as a revenge against her for telling their parents he had beer in the house, but obviously there's more to it than that. The way Cam and Greg see it, it almost seems like you think he did it as a kneejerk reaction of "justice." I'm pretty sure you're all familiar with the concept of sibling rivalry; that played more into this than the beer incident, I'd think. We don't know enough about the situation to judge wether or not the brother was in the right or wrong, and as such we shouldn't try to, but we do know that the sister is a closet slut with a reputation as a sweetheart, and that she bitchishly ratted out the brother for having beer, or at least that's the brother's perception of the events. It seems to me most likely that the brother doesn't have as good a reputation, due to the way he talked about what everyone thought of his sister. If he's sitting there struggling with bullshit from everyone for things he's done or how he acts, and those same people are patting his sister on the head when she's an absolute fucking whore, then I think exposing her for what she is is pretty justifiable. At the same time, the dynamics of a sibling relationship don't just develop immediately, they build up slowly, and as such, it's pretty rare to just have a total, unprompted attack on the other. The sister probably ratted out the brother because either the brother did something to piss her off or she wanted to get on the parents' good sides. Then you have a brother who has all the motivation I talked about earlier, and now a specific reason he's upset with her, and an opportunity to get some revenge on her. The revenge was triggered by the beer incident, but the factors that lead up to it and drove it were much larger and longer lasting.

You can say that he ruined his sister's life and all that, but really, all he did was show their peers something she had made and something she was doing. It's not like he forged the list or anything. And it's also not like her whole life is ruined, as Rydog pointed out, she's pretty fucked until college, and in addition to that, a lot of the shitstorm would've blown away after a year or so. In the brother's defense, the situation that I think existed where he was being lined up to his sister and everyone was saying how sweet and wonderful she was; that's a pretty motherfucking shitty teenage experience, too, and it's a result of his sister's false identity, as opposed to having something he was doing put into the open.

Of course, I made a lot of assumptions in what I said, and they could all be wrong. But the thing is, there isn't enough information here to gauge how right or wrong either party was in there actions, you shouldn't condemn or congratulate people when you have to fill in so many blanks to get an idea of the situation they were in.