Know what really irritates me?
People who insist upon diving in front of me as I coast to a red light and then pause for several seconds when the light turns green, often forcing me to brake when that would not otherwise be necessary.
People really need to learn to time lights on their regular commutes.
These same oblivious types who insist on getting in front of me before reaching an intersection will then drive well below the reasonable speed on the rural two-lane that involves about fifteen miles of my twenty five mile commute. This road has a posted limit of 55mph but is easily and safely driven at any speed up into the young sixties. It's wide and smooth with few blind hilltops or corners and very good sightlines at every crossroad.
These are the same folks who get in the way on the interstate, since they can't seem to grasp the simple concept of drive right, pass left. They think nothing of sitting in the left lane for miles on end even though the right lane may be clear for many hundreds of feet. In a lot of interstate driving, the fools in four wheelers do as much or more to create unnecessary congestion as do the larger rigs and people towing their toys.