A lot of these are very good, and I look forward to reading this thread for a long time.
I would say that if your reaction to a dangerous driver increases the danger for that driver, yourself, or anyone else, then you are not as good a driver as you think you are. Examples ITT include not letting someone in who is pulling a dick move, passing a dangerous, slower driver on an onramp, and hitting the brakes to "punish" the driver behind you.
johnny_on_the_spot, can you please do an AMA? I have a lot of pent-up questions about what the road engineers were thinking.
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I was about 3rd in line in the right lane at a red light. The front car in the left turn lane had her right turn signal on, so I'm thinking, "Fine, she got in the wrong lane, and is now signaling. Better than just gunning it with no signal." The light turns green (with a left arrow as well), and she makes a left.
She was yakking on the phone, needless to say.