Our Friday PCMs always touch on this subject.
Who's the worst? I don't know if it's the teenager texting while driving or the grandmother driving with her dog on her lap. Just last month I pulled up to an intersection and the driver in the car next to me was playing a guitar while driving with his feet. He had a folk guitar and was using both hands to play while operating the steering wheel with his feet. Needless to say, that license plate was turned in to the police.
Actually, the worst (and I apologize, DS, but this is true) are the Canadians who come down for the weekend. I am certain that some of their indecision comes from not knowing the area but some of the behavior just cannot be explained and the examples are too numerous to list here.