So, some guy tailgated me for about a mile and a half and then when I was turning left he drove real close to my car on the right and yelled "asshole" out the window at me.
While I don't defend the inexcusable slur, did you wonder what you had been doing wrong to provoke it? Road rage is a thorny issue, and it's not as simplistic as some people think... people have radically different approaches to driving from each other yet everybody has to share the same road... it's one of the few situations in our loner society where we actually have to think about other people.
One of the major causes of traffic congestion, for example, is people driving slowly in the left lane, or driving unnecessarily slow in the first place. Usually the people doing the latter have a 'my car is my castle' type attitude and take offense to anyone tailgating, honking, or encouraging them to move over. In other words OP, if somebody's tailgating you, your first response shouldn't be 'I should write a SF post about how mean people are', rather, you should move the f-ck over cuz you have no idea what the hell his situation is. The fact that he found it necessary to yell asshole though probably means he is one.