I haven't read the book but I can imagine some of the things a messenger has to say. And for the most part they are some of the worst bikers around. At least in Vancouver and Toronto (both places I have lived). I think a number of the problems roadies have with drivers in big cities is predisposed because of violations done to them at the hands of a messenger in a rush.

Not to say drivers aren't guilty too but messengers do everything drivers hate. They seem erratic pulling out and crossing when they need to at high speeds. While the biker may think he is in control the driver can't and won't know that.