Or worse, the ones who don't pull up to the stop line and so never trip the sensor to get the green arrow!
Why on earth do they need more than a car length between them and the stop line?!!!
Oh, or the ones who turn on their turn signal AS they are turning, not before hand.
I agree with hypatia on the ones who wait until the last minute to merge and then clog up traffic expecting someone to let them cut in (and someone always does let them in), even if there are miles of warnings to merge ahead.
Or the nitwits who don't accelerate when entering a highway on the merge lane, and then cut in front of you so you have to slow down (or else they slam on the brakes last minute so nobody behind them can get up to speed for the merge either).
Or the ones who drive 15 mph under the speed limit for no reason...always in the no-passing zone or left lane. Or worse, they move out into the passing lane and then pace the car they should be passing!