Here in Seattle, if I feel unsafe to stay in the bike lane, I can legally "take the lane." I make full use of the law where I see fit for my safety and wellbeing, all while maintaining traffic flow and keen awareness of others.
I can only remember a couple times where I was either honked at or yelled at from behind. I remember both occurred as I approached a red light. The driver behind me really wanted to speed up to that red light. This actually happened to me a couple times in Houston while I was driving. I wasn't going fast enough in approaching a red light. Some people really have to get to that red light. They have no use in smooth, fluid movement or trying to time the light perfectly to avoid a full stop.
Every other time a strange driver has yelled while I was on the bike seemed due to bad chemicals, gross immaturity, or personality disorder. So I can understand the middle finger response.