In the movie the car is shown to be evil from creation; in the book it is alluded that the previous owner's ghost drives the power of the car. Being based on Stephen King logic, it is safe to assume the car WAS created already infused with the dark spirit that seeks love and rage...lots and LOTS of rage apparently. This kind of explains why it kills the first person to ever sit in her after being offended by his cigar.
In the book, they take down Christine with a tanker named Petunia. In the movie, they take her out with a bulldozer. In the US, most heavy construction equipment is manufactured by Caterpillar, and abbreviated as "Cat".
In Stephen King's other famous novel, It, the eponymous clown summons a Plymouth the exact same make and model as Christine, who is driven by a dead guy. Let it sink in as to what that entails...
A car very similar to Christine also shows up in 11/22/63, driven by Sadie's psycho ex.
The death of Darnell in the film may seem weird in regard to the song used, "Bony Moronie" by Larry E. Williams as Christine is crushing him. It's Fridge Horror in two regards: 1. she's pretty much letting him know that she's going to crush him to death before she's does it. 2. during the crushing, she's mocking him for being a fat bastard.