Both Cera's Nick Twisp and Portia Doubleday's love interest are adorably pretentious teens, who drop vintage names and defend their sense of themselves with a sense of superiority; both the lower-middle class child of divorce and the girl with the churchgoing parents get prissy and defensive whenever they sense a challenge from the world they mean to reject before it can reject them.
Cera especially, because he seems so self-deprecating and virginal, is meant to be sympathetic; we feel for his unrequited love, or at least frustrated horniness, because we all like to think of ourselves that way, as secretly more worthy than the world gives us credit for being.
Now, this may come as something of a surprise to you, given that I'm a professional film critic and everything, but I didn't really date very much in high school. At the time, I chalked this up to the same thing Cera's character does: the world, in particular its population of teenage girls, doesn't know how to appreciate me yet. For now at least, the world thinks it's desperate for the shallow affirmation of arrogant jocks.
This attitude is, of course, a very deep kind of vanity. It's surprising, isn't it, when you grow up and discover that, even as much of a suffering sensitive nerd as you fancied yourself to be, you're just as capable of any lacrosse player of being mean, manipulative, self-centered, and so on. Maybe unattainable teen girls just pick the better-looking jerks?
At the outset of the film, Nick Twisp wonders why nice guys never get the girls; at the conclusion of the film, having contrived an alter ego to help him get in touch with his inner asshole and win the girl, he discovers that "Nick Twisp was enough" all along. The way Arteta closes in on this sentiment, it's meant to be somewhat heartwarming.
But here's what Nick Twisp does in the film—he wrecks both his parents' cars; he and the girl manipulate their parents to be together; he further manipulates dimly witting accomplices to get her kicked out of boarding school.
He's goaded, yes, by his alter ego, that smug Euro asshole in the white pants, but comes on. (The fact that his id gives him license to at last lash out at both of his divorced parents seems significant—like, yes, obviously, the calls are coming from inside the house.)
Youth in Revolt closes by rubber-stamping the lesson its protagonist thinks he's learned: someday, someone will love you for who you are. But the conclusion Arteta should draw from his material is: you're not as lovable as you flatter yourself to think.