For the last few years my job didn't take me very far (quite literally, it was about a five minute walk). However, in July I started a new job with the added bonus of a daily commute. Admittedly it's a relatively small commute of about twenty minutes, nonetheless it still involves cars and traffic.
Driving to work everyday was the first time I was regularly enraged by other road users. I'm assuming this is because I drive to work with a time limit, whereas in most of my other journeys I wasn't rushed at all. Suddenly almost every driver, in my eyes, was making dangerous and unnecessary mistakes. Inevitably, this invites an array of obscenities on a daily!
Speed
If a driver is speeding in front of me, I couldn't care less. If someone wants to drive irresponsibly away from my car it really doesn't bother me. Conversely, I become infuriated when a driver is two metres behind my car when I'm driving at a safe, comfortable speed (most likely the speed limit). In fact, I find I find it so distracting I'll usually pull over and let the vehicle pass. I was caught by a mobile speed camera driving 37Mph in a 30Mph limit. I attended a Speed Awareness Course, which was surprisingly informative and enjoyable, and since then I speed much less often.
Cyclists
The law needs to decide whether bicycles are road-worthy vehicles or not. Swerving in and out of traffic, on and off the pavement with useless lights is not acceptable. As much as I want to love cyclists for their commitment to the environment and what-not, I can't help but hate them. Cyclists with cycling gear, effective lights and knowledge of the highway code are hard to come by (a red light means stop, folks). Don't get me started on parents who cycle with children in a seat on the bike, or worse parents who cycle in tandem with children. It's incredibly dangerous.
Indication
If you are turning left, indicate left. If you are turning right, indicate right. I have no idea why some drivers find this so difficult to understand.
Elderly Drivers
I don't want to generalise, so let's be clear that most older drivers use the road safely. However, there's no denying that one's sight, hearing, and reactions all become less effective with time. According to the Insurance Insurance Highway Safety, a senior citizen is more likely than a younger driver to be at fault in an accident in which they are involved. Obviously they don't want to hear it, but we all know it's true.
In all honesty, I could write this list forever. I know I'm not the only driver who feels this way; it's no wonder I choose to drive at night for a more pleasant journey.