The only time I've had altercations with motorists was when I was taking the lane.

The first time, I was on a one-way street, 3 lanes, I was in the right lane. There was NO bike lane, and a line of cars parked along the curb, so I was riding "as close as practicable" to the right, which in this case, meant taking the lane. A car was slightly ahead of me in the center lane (to my left), and I was riding in the center of my lane, when a car came up behind me, then partially changed lanes to squeeze between me and the car in the lane next to me. There was NO reason she couldn't have just changed lanes and gone around me if i was slowing her down. Oh yeah, if it matters, she was one of those Volvo-wagon-driving liberals. Go figure.

The second time, I was again on a one way street, this time two lanes. Same situation, no bike lane, and a line of cars parked along the curb, so I took the lane, riding in the center of the lane. A car came up behind me, then changed lanes to pass me. It arrived at the stop sign less than a second before me, and from the way it was angled as it approached the stop sign, I could tell he intended to turn right from the left lane. I pulled up alongside him before he could turn, stopped, looked at the driver, and asked him "What are you doing"? I then proceeded to go straight, and he decided to make a legal turn at the next stop, instead. Not really endangering me this second time, but he would have if he had been able to beat me to the stop any sooner.

I've never had any negative interactions, otherwise.