You don't meet them often but when you do you know it. 
I met one yesterday. An idiot driver who somehow thought the appropriate way to pass someone leading a horse is to scrape by as close as possible beeping the horn. Fortunately my mare was v. brave and well behaved.
Why do some idiot drivers do this??
He also swore at me and shook his fist. Fucking idiot! I am afraid I used bad language and gave him the finger.
I have also been googling to try and find the contact details for the company painted on the side of his car so I can phone up and complain.
Haven't found them yet as I did not see all of the name.
Bastard.