Frustration
Crash's experience of reality is shaped by the imagery of frustration and desire. He is frustrated because he wants something that makes him feel embarrassed; he wants the love and support that Penn gets which makes Penn such an open and supportive person. The frustration makes him swear-off friendship with Penn. They become social rivals, but that only worsens the dilemma, because as time goes on, people like Penn more, because he's actually respectful and kind, whereas Crash is angry and unknowingly aggressive.
Competition
Crash would say he is not aggressive. He would say he is competitive. That is also true, but so is the first one. His competitiveness is explored through the imagery of his friendship with Mike. Mike Deluca is also competitive and edgy. Both are cool automatically because they are competent athletes, but neither are powerful enough to mitigate their competitive tendencies. Instead, those tendencies are amplified, so that Crash becomes an unnecessarily competitive person. He competes even when Penn is not competing back.
Personality dynamics
What is on display in this novel is personality dynamics. We have already seen how Crash's personality is amplified and darkened by his dynamic relationship with Mike. This shows that Crash is dynamic, which is good, but Mike is not dynamic, so that relationship becomes toxic and unhealthy for Crash's life. His personality dynamic with his crush, Jane, is also warped because everyone knows he has some unfair beef with Penn. Jane—and Crash's own younger sister!—just love the kid.
Aggression and violence
Crash starts the novel as a competitive and athletic person, but through the course of the novel, we see him venture into a pretty unsafe and chaotic part of his personality. He becomes explosively angry, and his aggressive, teeth-out personality becomes a threat to others. His discovery of his own violence leads to an outburst of violence, not against Penn, but against his own ancestor, his grandfather who later dies. This feeling of guilt is punishing enough to make him repent of violence, and he even backs off competition too, letting Penn win.
