As a driver, cyclist, and pedestrian, I've had more than my fair share of bad drivers.
Tailgaters - especially when the passing lane is open. I was once tailgated dangerously close by a bus when on a bicycle, even though I was barely under the speed limit and had to pass through short section of road where there was no bike lane. I've also had semis do it to me on the interstate/motorway (in a car, of course), and that is just dangerous - at night when they are blinding you with their lights, it's even more dangerous.
Honkers - On the bicycle, I was once honked at by another bus driver in the same section of road. Legally, a bicycle is a vehicle, and I have every right to the road as you do, and if you give me a few seconds, I'll let you pass when we get to the section of road that allows you to safely do so. I've also been honked at for no apparent reason at all (also on the bike) despite being in the bicycle lane and out of the way.
Drivers who block the bike lane/sidewalk
"Weavers" - people who weave though traffic across multiple lanes, especially those who do not know how to use their indicators/turn signals
Cell phone users - those who talk or text behind the wheel
Drivers who do not yield/give way to pedestrians in the crosswalk.
Thumpers/rattlers - Need I say more? If the stereo costs more than the car, you obviously have problems
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"Tongue tied and twisted, just an earth-bound misfit, I" - Pink Floyd
(and then the tower cleared me for take off)