How does the author portray Dell in a negative light in Chapter 11?

In Chapter 11, the author portrays Dell as even more despicable than in prior chapters. Dell picked up a cat he read about in a lost pet ad just to try to impress Willow by calling it his, and when the cat ran off, he seemed completely unconcerned. When Dell drove back by the school and saw it sitting in the parking lot, he didn’t even stop to pick it up.... he just left it to fend for itself.