I agree with this OP and wish to subscribe to supergalactic’s newsletter.
I’m not gonna weigh in on whether or not OP is tailgating, but I will say that I have no love reserved for people who swerve left just before turning right. None. At. All.
I was looking at the road as I walked to get groceries today, Frank, and I think you’re right - I got a little carried away saying you can never cross one.
I hate the swing left turn right thing, too - one of my extremely few fender benders was caused by a new driver signalling to turn left, then swinging so far right that I thought she was parking on the street. My years of driving actually worked against me - I ignored the signal and went by what the car was actually doing and passed on the left - just in time for her to swing back and clip the rear panel of my car. Lesson learned - if what they’re doing and what they’re signalling don’t match up, hang back and let them sort themselves out.
I was imagining an unusual place where people drive miles and miles down a two-lane highway with houses every few hundred yards, just to turn around after the all-powerful never-crossable double yellow ends so that they can come five miles back home. 
You have to drive as if the person in front of you could slam on their brakes for no reason at all, and still be able to stop in time. Especially when operating a heavy commercial vehicle with longer brake time than a sports car.
I work in commercial auto insurance, and if you ever hit one of the people pulling the sneaky driveway maneuver, you **will **be found 100% at-fault. In case you weren’t aware. Yes, what they’re doing is stupid and a dick move, but clearly it is happening to you frequently enough to warrant posting a rant about it. Drive doubly defensively when you’re on the clock, or you could risk losing your CDL. Not worth it. In the eyes of a claims adjuster, you’re continually engaging in risky behavior: tailgating.
That may be the party line, but I am pretty confident that if I stomped on my brakes on any random highway or street around rush hour in New Jersey I would be rear-ended. And we all know the guy in the back is 100% responsible.
That doesn’t mean that people shouldn’t have a degree of personal responsibility for awareness of what is behind them. For example, when I am changing lanes in front of a truck in heavy traffic, I typically let the signal click at least three times before beginning the move since I want that driver to see what I’m doing and not be surprised.
Likewise, if I see a big truck behind me and I see a slowdown ahead, I will tailor my braking accordingly.
Ever since I started driving I have disliked the “rear driver in a rear end collision is always at fault” mantra. I had barely been driving for six months when some butthead cut me off on a snow-covered Michigan highway and slammed on his brakes. I slid off onto the shoulder, narrowly avoiding smashing into him. I was shocked when folks later told me that I would have been fully at fault for that bozo’s stupidity.
Situational awareness is important. Sometimes it can even save your life.
When I have to come to a complete stop on a highway due to traffic, if I happen to be the last car in line, I always leave about a car length of space in front of me. Stupid, right? Well, not so much. One time I saw a truck in my rear view mirror that was barreling toward me and didn’t look like he was prepared to stop - at least not in time. I popped the clutch and lurched onto the shoulder. The truck did end up stopping but I noticed he was occupying the same space I had occupied previously.
Back to the OP. This is one reason we have roundabouts and no-right-turn signs (U.K. - we drive on the other side). Instead of crossing the busy lane of oncoming traffic, you go on to the next roundabout, turn around, and then safely turn into your destination.
Perhaps the OP should write to the relevant authorities and suggest this as a safety feature.
And I thought that backing out onto a main road was illegal: you reverse into your drive.
In the DC area, late signaling happens “rarely” only in the sense that a lot of people don’t signal at all, thus escaping the stigma of having signaled “late.”
Seriously, people, it should be renamed an intention signal. Too many people seem to think it’s a “turning” signal, as in “use it once you’re into the turn.”
My hope is for smart cars that will allow a driver to turn the wheel without having signaled in advance, but will electronically deduct a fine from his bank account when doing so.
People turning into driveways don’t necessarily live there. They also don’t necessarily know where the place is located, if it’s a business driveway. We deliver meals on wheels and sometimes do unfamiliar routes when needed. It’s quite common to have to slow down to search for an address and suddenly see the driveway behind a hedge. Last minute turn signals in that case are unavoidable. I’m sure it pisses people off, but tough shit. Stay off my ass and you won’t have a problem.
The other guy changed lanes (or turned) improperly, in this case. However the fault determination could go either way, depending on whose side had better witnesses.