It's typically some chubby peckerless type in the truck. I take solace in the fact their fat azz will likely stroke out before age 60.
I do not know the motivation of that particular driver, but I can say that those bicyclists that spread themselves out over 10 miles of narrow, mountain roads have a tendency to back traffic up considerably, and piss a whole lot of fugging people off.
And for all you motorcycle guys that like to tour the west? Bunching up in packs that stretch 10 vehicle lengths, while driving 15 under the speed limit? Yeah... there's a reason people hate you.
Travis