Ok, I'll say it - bicyclists tend to annoy me. Obviously, I don't shout at them, or try to hit them, or make them think I'm trying to hit them. That's nuts. That seems like a problem separate for bike/car relations. I doubt someone who behaves that way in a car gets out of it and suddenly becomes a calm and reasonable person.
But here's my assessment of why bikes annoy me. Not argument that they should, just some introspection.
* They make me nervous. Cars are easy to see, have lots of momentum to overcome, and generally exist on a predictable well defined plane. Bikes are different. They can enter the car plane from places I don't expect and didn't even realize existed. They can make 90 degree turns on a dime (relative to my sedan) and can stop in inches. They don't generally obey traffic lights, stop signs, one ways, or any of the other rules that lend predictability to car behavior. They don't have brake lights or signals. And in a complex driving environment, they're tiny and often poorly lit. They also have no protection. Slow moving car crashes aka "fender benders" are expensive and annoying, but rarely dangerous. Similar accidents involving a bike can end lives. Having a bike near me makes me worried I'm going to hit it. I don't want to live with that so I give it huge space and pay it lots of attention. If I could drive on roads that didn't have bikes I'd prefer it.
* Civic disagreement. The arguments in favor of making roads more bike friendly are generally: more healthy, more space efficient, more environmentally friendly. I agree on healthy and environmentally friendly. Though, it does seem odd when someone tells me biking is super healthy and super dangerous in the same sentence, but I cede the point. Space efficient? Yes and no. It is more space efficient for people whose options are bike vs car to ride a bike, but there's tons of people that doesn't apply to - people who live far away, people who need to haul things, people who have health issues, people who are too young etc. Also, lots of people don't want to bike in heat, rain, snow, etc. Also, not everyone has a place to change and shower when they get to work. The shower issue and the distance issue disproportionately impact people who are less well off. I get that biking can be part of the solution, but man does it get over hyped.
* Guilt/jealousy. I really enjoy biking! If I'm in my car and you're on your bike - I'm pretty sure you're having more fun than I am, and that makes me jealous. Then I start asking myself why I'm not biking, and sometimes the answer makes me feel guilty. Neither of those emotions often get followed up with - let's arrange it so I can experience more of this.