I nearly always use my turn signals, except in a few situations. Such as when I forget my turn/exit is coming up, I'll still use the blinker but its usually only a second before I make the turn.
What bugs me are car horns. They serve no useful purpose other than to annoy. For example, I my apartment is on a four lane road, two lanes in both directions. I typically have to make a left turn into the complex. There is a left turn lane, but its only a partial lane, as its the opening part as you approach a nearby light, I'd say you have maybe 3 feet of left turn lane at most. So, as I approach the left turn, I'm in the left lane with my signal on, moved over as far to the left as I can without being in the oncoming lane. Simple logic would dictate one of three courses of action for traffic behind me. 1) Change to the right lane and pass the vehicle signaling for a left turn(me) or 2)If the right lane is not clear for a lane change, slow down until able to make a lane change, or 3) If unable to make a lane change before impacting the car turning left, stop and wait until either the car is able to complete its turn or you can change lanes and pass.
For some reason, this is difficult for a lot of people, who have tendency to stop inches from my bumper and honk their horn continuously until I complete my turn, where they then floor the gas, usually so they can wait at the red light about 200 meters away. I've had people also try to fit between my vehicle in the left lane and the car in the right lane. Motorcycles love to do this, but they can at least fit even if it is still illegal and stupid. I've seen 4d sedan's try to pull this stunt off.
This might more sense if I were to draw it out, but I'm lazy and tired now.