Ok, there are some right eejits on the road and some who do not deserve a license at all, but it seems to me that when someone 'cuts you up' or 'doesn't indicate' then it's our reaction to that which is more likely to cause an accident.
Yesterday, a woman actually drove alongside me on the motorway and continued to stare at me, shaking her head and making hand gestures (for what seemed like ages) surely this behaviour could have caused more of an accident than me joining the motorway behind a slow moving vehicle and moving into the middle lane way in front of her to take over slow vehicle? And when I did this there must have been at least 200 yards space, the woman obviously took exception to my being in her way...
Obviously every occasion is different and should be treated as such, but it really bothered me that this woman was so enraged by such a trivial thing, and continued to endanger herself and others on the road!