This thread has given me some perspective - thanks for all the responses - and I'm still searching for an approach that works for me. But this is how I currently attempt to approach bullies on the roads:

I absolutely refuse to be bullied off the road and I refuse to even acknowledge the horns, obscene gestures, and yells.

This has been hard for me in practice since I have an overdeveloped sense of justice. My instinct is to give them the finger right back or chase them and tell them that I have just as much right to the road as they do. But I've discovered that that doesn't do any good and I usually end up feeling worse about the situation. It's still a drag that there are jerks out there who think I am a jerk for merely doing what they are doing (using the public roads to go to and from work) but I'm no longer going to let them ruin my ride. Instead I'll vent here!

So here goes with the venting:

• Isn't it strange that when there is not enough room to pass safely it is the fault of the person driving the vehicle that takes the least space?
• Isn't it strange that when there is not enough room to pass safely some motorists think their only choice is to pass unsafely? It doesn't seem to occur to them that the safe and legal solution is to wait until it is safe. I actually had a motorist tell me that he had no choice but to squeeze me out!
• Why do some drivers insist that I use a bike path that is one way in the opposite direction?
• Where did that jerk motorist get the idea that "If you're in the road, you're part of the road"? What does that even mean? That I am considered a speed bump?