1. People who are actively malicious (either they're fed up of being "held up" and decide to teach you a lesson, or are c*nts who think it would be amusingly Tom and Jerry like to throw stuff/shout at you/push you) being too stupid to realise how dangerous this is).
2. People who haven't read a higway code since the old king died, and are convinced you shouldn't be on the road (ergo you deserve no consideration).
3. People who are inattentive. They have converted their car into a smaller version of their house (lots of cuddly gonks, and or stickers) and pay as much attention to the road ahead as they would do when sat in their house watching Corrie. May be eating crisps and.or answering the phone and texting during either activity.
4. People who are "skilful" and decide to demonstrate this by driving quickly, weaving through traffic, and passing too close. Perhaps they are pretending to be stuntmen.
What people are driving is a bit of a red herring really (although gonks in the window, excessive body kit, and the logo "Range Rover Sport" or "BMW" put me on my guard, perhaps unreasonably so).