Drive around your town or metropolitan area on any day,
keeping in mind that driving a motor vehicle is the most complicated mind-body action most people perform, and observe the following practices: failing to signal changes of direction regularly or at all, especially turning right; failing to make a right turn if an approaching vehicle is in the same block; turning left from two lanes wide or so slowly as to impede following traffic; changing lanes with insufficient warning or none at all; and stopping at roundabouts when it is safe to proceed (demonstrating ignorance of their purpose to keep traffic moving, or lack of confidence in interweaving with other vehicles).
Less dangerous, but still annoying to other road users, are drivers who show absolutely no awareness of following traffic, who have no feel for the spatial limits of the car they are driving, and who cannot park near the kerb or in a single car space.