Two related posts. Jeremy, you have clearly forgotten what teenagers are like. They can change abruptly in a very very short period of time. They can go from being incredibly happy to morbidly depressed in a simple 5 minute time span. So I'm sorry if you don't think such massive swings are possible in a mere three months. You're wrong. As Tim noted, there's also a very definite self-absorption factor here, where kids like Will don't have the ability (or willingness) to look at the other side of the situation. These are not always pleasant traits, and they don't tend to endear a character like Will to readers, especially mature readers who have limited recent experience with bratty teens. I'm not trying to make him endearing. I'm not all that concerned with whether readers like Will or not. I think when he matures, he'll be a really neat character. Right now, he's rather annoying. I think that's realistic.
I also think that he has some definite grounds to be bitchy, so even though he may be annoying and self-centered, his points, I think, are valid. Again, kids his age don't always communicate in a productive way. If I wrote him in a way such that he addressed issues in a rational manner, I'd get howls from those who know what these young creatures are like. Again, I was going for a more realistic portrayal.