Not every time an officer is going on a call do they use lights etc. such as a non emergency. The person in front of him did a few things wrong and it showed by their deer in the headlight reaction. If someone, especially an officer comes up on you, move over. In this case the mere presence of the officer froze this persons decision making process, it is that type of driver that causes accidents and somehow drives away oblivious and unscathed. If you don't have the mental capacity for that situation, then what if that driver really needs to think fast? I have seen a state trooper do this on a major highway here. A box truck doing 60 in a 65 had himself right next to another car for a good 5 miles with, not only the SP behind him but a row about a mile long of backed up traffic. The only way he got the truck over was to throw his lights on.
There is also the possibility that that driver, who by the way had no business in the lane, may not have looked in the mirror even once to know he was even there....scary.
The other ones that are a nuisance are the self policing crowd. The "I'm going 5 over fuck him" crowd that ends up looking in the mirror at you more than the road ahead. If someone wants to go faster, let them.