You forgot "classism."

To me the worst kind of driver is the inattentive one. The ones that are not paying attention because they are, texting, talking on their cell phones, eating their #2 combo, putting on mascara, etc. It doesn't matter what kind of person they are or what kind of driver, good or bad, their distracted driving will assure that you as a bike rider will not bee seen by them which is crucial to your survival on the shared roads. Other drivers are affected by these type of people too but at least that have a steel cage around them for some protection.

I despise indecision.

When riding I base all my navigation on years of anticipating where certain types of people and or vehicle will go. When someone has indecision and I can't act it becomes dangerous. Simply put I have no problem swerving to avoid X, but if I can't have enough data to decide left or right in the half second I have, it pisses me off.

My area has a camera where an accident happened. Unfortunately the photo was of such poor quality it was utterly useless. The local paper ran a front page article asking the public for help identifying the vehicle after 3 months. My coworker and myself came up with 5-6 possible cars based off the photo. The sad thing is my coworker knew the guy who was injured and I ride past the spot everyday after work. I wonder how much our county payed for a worthless piece of equipment?

Ageism / sexism incoming: 80+ year old ladys. Twice ive nearly had them run me off the road. Worst time was when two of em were in a car together and they started laying on the horn as they passed. Nearly caused an accident with me and my dad.

The red-neck stereo-type has proven two opposite ends on some occasions. One time I had them spit at me and try to door me. Other times they have stopped pulling out of a parking lot and backed up to let me pass and added a kind nod just to spite me

I would have to say it is really up in the air. Worst drivers are either rushed drivers or inattentive drivers though.

Rain seems to induce both on a good number of drivers though.

a vote for bmw & lexus drivers.

A vote for older luxury car drivers.

The most inconsiderate drivers that I've encountered have usually been driving imported luxury vehicles. Especially Land Rovers and Volvos. Yobs in pickup trucks come a close second.

Perhaps there aren't as many sport cars on the road here, but 'real' sport cars (as in not rice rockets) don't seem to be as inconsiderate.
For those that are with expensive cars, I should mention that a benefit of commuting with clip-less pedals and cleats is the ability to leave a scratch while on the road.

I live in a college town. To me, that means two things. One: All of the students (including me) who bike or walk respect each other. And two: "Townies" (residents of the town) have no tolerance for bikers on the road.

Our last mayor did a stellar job of getting bike lanes put downtown and advocating the share-the-road mentality overall. Nevertheless, in this town, I have to say that the worst drivers are other students.

If I'm on campus or downtown, I seldom get harassed. But when I'm on one the roads that connects the surrounding 'burbs with the hub of the university, I need to watch my ass. (A lot of students live south and east of campus, then drive to class.) During the summer, when the town was a lot quieter, I didn't get bothered. Within two days of people coming back in August, I had several drivers yell at me to get on the sidewalk. Stupid, since "walk" is in that word. Also, getting yelled at tends to startle me when I can't see it coming.

So yeah, my vote is for intolerant, hormonal young drivers.