Not surprised at all with the motorists' getting in a state, they really do hate having it pointed out that just driving in between two lines simply isn't enough. I know when I drive I'm all over my mirrors every few seconds, with preemptive signals and full look out the window check whenever I change lanes. It does seem to be too much to do all at once for many of the drivers I encounter in my urban riding commute. I'll stare in the passenger window for several seconds sometimes as we share speed and for the most part, their eyes never leave the bumper in front of them. Once comfortable with driving it seems the defensive driving tricks taught to them early on are lost. Just don't tell them that.