Most people are not bad drivers on the whole (although there are some exceptions). I would be everyone has done something wrong/stupid at some point while driving though.
By bad I mean those that have no idea about things like roundabouts and when to give way for example. People who think that it is wrong to look prior to actually arriving at a junction and then stop anyway even when they don't have to, people who think if there is a 1 degree kink in the road they must do an emergency stop to get round it. etc ect
I like to think i'm a good driver and have been told so by friends and that. My Dad has always been an excellent driver and I think I take after him with things like hazard perception. He says that if i make sure i do everything right, it's just the other people i have to worry about.
Did some major motorway mileage over the weekend and the number of idiots you see is incredible. People leaving the middle lane to move into the fast lane and entering gaps little bigger than their vehicle!
The major problem is - all the time you learn, there is an experienced driver sitting there stopping you from getting into bad habbits.
The day you pass your test, that 'filter' is removed.
So a lot of people get into seriously bad driving methods, but they never know they have because no-one ever tells them, so they blythly assume they are as good as the day they passed.
Human nature dictates that everyone else hooting and flashing just means they are the bad drivers!