An enemy forewarned is an enemy forearmed.
I agree we should signal but there have been rants on this board about people who speed up to prevent you from changing lanes.
Meh. Signal, don’t signal. It’s all the same to me. I saw you coming anyway.
But to directly address the OP, I also wonder what’s going on in your example driver’s mind. Maybe it’s a case of, “but officer… I DID signal”. More likely is that he’s got one finger on his phone, one hand on a cigarette (or cheeseburger) and a knee holding the wheel. Viewers should consider themselves fortunate that they saw even a flash of turn-signal coming out of such a scenario.
Ah, hence the phrase, “the dance of death.” 
If your dancing is killing people, don’t dance.
Again, that’s not my point. I should’ve been clearer in the OP: I’m talking about traffic going the same direction you are. As in they’re just ahead of you. The post about laziness is the the one that fits what I’m talking about.
As for the bolded part above, I know where you’re going, because you started to change lanes. It’s unnecessary, to put it mildly, to signal when you’re halfway through a turn. Or just as bad, click your turn signal one time through the turn. Why bother then, when it’s just a half-assed attempt to tell people what you’re doing?
On the other hand, I once saw a motorcyclist riding down the road talking on a cellphone, so it’s not like I should actually expect people to consider what they’re doing when they drive. I used to point out mistakes to my mother when she drove, and her response was, “Oh, they’ll watch out.”
I thought I did address your point, though. Paragraph B, above 
I always use my turn signals properly, at my age that means left hand on all the time.
I usually signal my lane changes. I find a good spot to get over, flip my signal and make my change.
I however, also psychologically profile the drivers around me, and if I think that turning on my signal is going to make the car behind and beside me close the gap so that there is no longer a safe space to merge into, I do not.
I may have pulled in front of you, without signalling, if I thought you looked like the sort of person that would obstruct my ability to merge. If so, I apologize, but at the same time, with the large number of people that seem to have some sort of issue with the idea of someone driving in front of them, I will continue the practice of only using my signal when I think that it will be used as an indicator that I will be changing lanes, and that other cars should maintain their current velocity, rather than in situations where I know that if I turn on my signal, the car behind my intended future location will use that as a signal that they need to close the gap, making me miss my exit, or trapping me behind slow traffic.
What do I base this on? The kind of car you are driving, how fast you are driving, what kind of following distance you are leaving, whether or not you used your signal to get into the lane you are in, and how steadily you maintain speed and position in your lane. Am I wrong sometimes, probably, but I usually actually err on the side of using my blinker, and most of the time that I am on the fence about whether or not my profile is correct, and I use my blinker, they close the gap.
If you want more people to use their blinker, then more people need to stop thinking of driving as a competition.
How do you concentrate on the road when you’re entering all these values into your spreadsheet?
I don’t concentrate on the road, the road is predictable, and always goes the same way.
I concentrate on the cars on the road.
Who’s Todd Rundgren?
–Mick Jagger
Several years ago I drove a car with broken turn signals, so I had to use hand signals instead. Man, that got a lot of strange looks. Nobody knew what the fuck I was doing.
Never use your signals, it is a sign of weakness.
All you really need to know is that my car goes in front of yours.
If I know what you’re going to do, I’m less likely to hit you. Why is this a bad thing?
At one intersection near me where I turn left oncoming cars usually turn left, but can go straight. If they are turning left we can turn at the same time. If they are going straight I can edge into the intersection until they pass. What usually happens is that they don’t signal (even though I am) which makes me think they are going straight, and only start to signal when they start to turn.
I can only guess they think that the car won’t turn unless the blinker is on or something.
Northern California drivers are for the most part morons.
One of the outlets to my apartment complex has something even worse. It is small enough that if there are people waiting to turn out of it, people turning right into it will have to slow down for safety. If these people signal far enough ahead of time, I can either cut ahead or in front of them safely, but they invariably either don’t signal, or only signal a second before they turn, causing both me and them to lose time because I’m certainly not going to go in front of someone who doesn’t have a turn signal on and certainly not going to go in front of someone who has a turn signal on when it would cause an accident if they hadn’t planned on turning.