Marcus claims that he is done with Ronnie and that he only wants to party. Teddy and Lance have the booze, and Marcus has picked a rental house for his once-a-summer party. Marcus thinks about his fascination with fire — at age 12 he torched a barn, then a warehouse, then other buildings. The most important things in his life are booze, drugs, music, and girls.
Marcus feels confident because he knows Will's weak spot, though he doesn't say what that weak spot is.
Marcus' emotional response, "screw her," which he repeats, demonstrates the anger that he is feeling — he doesn't know how to deal with not getting his own way. Clearly, Marcus' relationship with females is the antithesis to everything that is developing between Will and Ronnie.
Marcus's history of starting fires not only develops his character but also foreshadows future events. This chapter serves to illustrate the extent to which Marcus is angry and maladjusted.