The majority of irresponsible drivers I encounter drive pickup trucks. I once had one speed up to pass me so that he could make a right turn in front of me. I locked up the rear wheel and bore down on the front and barely missed him. In another incident recently, a pickup truck driver passed me on a road with little shoulder. I swear his right-hand mirror missed me by about 2 inches. There are more stories, most of which I've forgotten by now.
The other bad lot are cars full of teenage boys. These guys feel all-powerful driving in their beat-up old cutlasses and dodge neons. They love to shout and jeer as they go by. I always am tempted to challenge them to a race on the bike! Of course, any type of mouthing off to such beligerent drivers has to in some way be backed up by a bigger stick, usually not present due to me being solo on a bike and them outnumbering me in a big car.
Pickup trucks are generally higher to insure. I think insurance companies have picked up on their higher rate of ignorant drivers. Even Lance mentions pickup drivers in Texas in his book.
I know plenty of courteous, good-driving pickup truckers. However, there are equally as many ignorant, macho ones who I think get a little extra pleasure teasing guys with shaved legs in tight clothing...