According to an article I read today on Mirror, we swear 41 times for every 100 miles we drive.  I've not metered myself, but that sounds totally possible to me.  In the article, they give a list of the top things that set us off behind the wheel, but without looking at that, I can easily tell you my top 5:

  1. Not using turn signals
  2. Sitting at a green light because they're not paying attention
  3. Not understanding how traffic circles work
  4. Not knowing the rules of a 4-way stop
  5. Driving through uncontrolled intersections without even looking

As a bonus, the other thing that gets me is people not understanding that going left on red from a one way onto another one way is perfectly legal.  I drive downtown a lot and at least once a week I will sit behind someone who is apparently unaware of this law.