People that hesitate too much, people that text and drive, short stoppers (meaning they either slam on brakes at the last second, or they unexpectedly stop short of where you think they will at a light), people that "also drive". I hate it when people approach driving as a secondary task, it's something that you also do while doing something else like talking on the phone, texting, doing makeup, etc. I once saw a guy with his phone in the crick of his neck between shoulder and chin, holding a cigarette and cup of coffee in one hand, and using the one remaining hand to go back and forth between steering wheel and shifter. The longer I watched him the more amazed I was that he could stay on the road at all.