1) People who don't indicate at roundabouts (whether entering or exiting)
2) People who don't indicate at junctions
3) People who do indicate, but, not until either AFTER they've made their maneuvre or right at the point that they're doing it....cheers for the warning
4) People who sit on your tail in the fast lane when there is a vehicle right in front of you....what do you expect me to do about it?!
5) Selfish pricks who fail to move out into the middle/outside lane when they pass a slip road where there are cars trying to join the traffic

Insert your top driving-centric frustrations below: