Courtesy is the biggest problem, most people don't take half a second to think about the repercussions of their actions. Too often people get caught up in the rules and having the right of way, rather than slowing down to let someone in or letting someone pass. In reality, it wont make their journey any longer - at most maybe a couple of seconds.
A couple of weeks ago, I was driving towards a railway crossing where everyone is required to zip merge into one lane. The woman behind me decided that she wasn't going to let me in, which meant that If i kept going, I would end up driving off the side of the road into an embankment. With a car behind me and a car in front of me, I had nowhere to go so I slowly moved in towards her lane, forcing her to slow down and let me in. She was waving her arms around in the air, flashing her lights, tooting her horn and giving me the finger.
After that when the road went back into two lanes, she sped past me through a red light/speed camera and the flash went off. Must've been in a hurry to be somewhere? :hmmm: It's pretty scary that people like that are given the privilege to drive.
So, anyone wanna guess what sort of car she was driving?