I used to be pretty hard nosed when it came to demanding my right to the lane, but I've noticed that good will toward drivers goes a long way, especially if you're on a route where you'll encounter the same drivers every day. If I see a car pull up behind me with its right turn signal on, I'll usually get off my bike, pick it up and move it the four or five feet to the left the car needs to turn. A grateful smile beats a menacing look any day as far as I'm concerned.