There's no way for us to know exactly what set off the initial chain of events. It's unfortunate, but apparently the horn was the trigger. When I was growing up in the sixties, a friendly toot toot from a car horn was usually perceived as a safety, hello gesture. But, boy oh boy, not in the world we live in today. Sure, using your horn to admonish someone who has cut you off is illegal. But in this case we're only guessing about the circumstances that initiated the cyclist flipping off the woman driver. Consider a different scenario. If the woman was attempting a legal pass and the cyclist drifted into her lane, for safety reasons she could then have legally sounded her horn. So, although she might not have been the initial aggressor, that possibility would have no bearing on the eventual outcome.
Just wanted to take a pass at how we all see the world from different angles, influenced by different life experiences.
Since we're sharing different life experiences, here are some of mine. I'm a driver, too. I encounter cyclists and pedestrians and have no problem passing safely. I do not get upset when I approach them every so often, just as I do not get upset when I approach a tractor driving down the road, or have to stop at a stop sign or a stop light when other traffic wants to pass. I recognize that I'm no more important than anyone else and I sometimes have to wait for others.
When I'm on my bike, I (very rarely) get a "toot, toot, hey I'm passing" type of honk, but, when I do, it is usually reciprocated with a wave and a smile. No reasonable person would flip someone off for that. Could that have been the case? Maybe. Likely? No. Drivers (very) often lay on their horns as they pass very closely to give a very clear sign of their disdain and disapproval of me on "their" road. Here are some incidents I've encountered while riding my bike, alone, in a straight line, as far to the right as possible, at about 15-20 mph, on a flat road - with no oncoming traffic and plenty of room to pass safely. I've had people half-pass and then swerve into me to try to run me off the road; pass and slow down to 10 mph and squirt wiper fluid, slow down and yell at me to get off the road. I had one guy in a truck approaching from the opposite direction, IN THE OTHER LANE, slow down and veer into my lane and pretend to attempt to hit me head-on. When you include the minor hills we have in Tennessee, people lose their minds if they have to slow down for 30 seconds to wait to pass safely. Honking, giving the middle finger, yelling and throwing objects are common assaults against cyclists around here. This kind of intimidation with a vehicle is akin to pulling a gun on someone and telling them to get out of town because they aren't welcome in these parts. Drivers constantly try to bully and intimidate cyclists to get them to stop riding on the road. And it has been working. Lots of my friends no longer feel safe on the roads. When they do ride, they rode in very large packs - making the delays for drivers even worse. A friend was hit by a truck towing a trailer who swerved into the pack and slung him into a telephone pole, almost killing him. His penalty was a minor traffic citation. Congratulations to everyone who has used their vehicle to threaten someone's life, you have likely won a battle against a bicyclist.
Some drivers are downright dangerous - making life threatening passes due to aggressiveness or ignorance. You want to know why cyclists ride in the middle of the road? Because riding all the way to the right encourages unsafe, in-lane, passing. Some roads are 12 feet wide, that's 144 inches. Most are 11' wide. Subtract the mandatory 36" from the cyclist and another 24" for shoulder width and you're left with 76". Car width is typically between 80" and 96", so unless your left tire straddling the center line into the left lane (yes, this is a perfectly legal maneuver - even when presented with a double yellow line), you are passing too closely. I used to ride far to the right of the lane, often on the white line. Cars and trucks constantly buzzed me, giving me less than 36" between 4,000 lbs of steel and my shoulder - without slowing down. All those incidents I mentioned occurred when I was riding alone with zero provocation, in a way that drivers claim they want me to ride.
I've learned that riding like that is LESS safe than riding the way everyone complains about. My wheels are in the same place in a lane that a car puts it's right wheel in the lane. I stick out my left arm as a car approaches. I wave them down if I see they are approaching too fast. You know what? Cars more often pass properly and safely when I ride like that. If drivers were more courteous, recognized bicycles as legitimate users of the road, stopped honking and passed safely, cyclists wouldn't be so quick to pull out a middle finger. I've also been riding with a camera and send video footage (of aggressive drivers who do not like my particular riding style) to the Sheriff or Chief of wherever the incident took place. They send Deputies and Officers to the residence of the offending drivers to let them know about the three foot law and potential prosecution for reckless driving. I encourage you to do the same with a dash cam. Feel free to PM me any footage you get of cyclists breaking any laws. I've encouraged many people to do this over the past year and I've yet to receive a clip.
As for drifting into "her lane," the cyclist would have had to have drifted into the lane across the center dividing line as the full right lane rightfully belonged to the bicyclists in front of her. Remember, cyclists have the right to swerve to avoid hazards in the road and may use the full lane. Is it probable that this cyclist swerved to avoid a hazard and drifted into her? Probably not as that likely would have been mentioned as the reason she honked.
Look at this thread and look at the comments from the original article. Contrary to more than 100 years of transportation law, many people feel bicyclists do not belong on the road. They feel bicycles are just entitled people playing in the streets and holding them up from getting real business done. Well, roads have always been a public good paid for by the general tax funds, like parks and schools. I have just as much right to lawfully operate my bicycle on the road as any motor vehicle. You often use the roads for recreational purposes as well. Your use of the road is not more important than mine simply because of the vehicle you choose to use. If I incur a minor delay upon you, it is no different than my having to stop at a stop sign to let you cross an intersection.
Here I am defending cyclists, who were operating their bicycles in a legal fashion, against some strangers who have sided with a man who caused a crash and then drove off. The driver is clearly at fault and some of you are trying to figure out a way to blame the cyclists. Do you not see how absurd this has become?