I would interpret someone flashing his/her lights as me as aggressive. I'm not in the habit of driving slowly in the left lane of a freeway but, at the same time, no one has the right to drive as fast as he or she wants.
I've also noticed that a lot of people seem to think that "slower traffic to the right" applies in all driving situations. It doesn't--just freeways.
That really depends on your definition of "freeway". Most commonly, the word applies to interstates. It can, by definition, also apply to any divided, multi-lane highway with access and exit ramps.
Where I am, slower traffic to the right applies on all multi-lane roads (to quote the ordinance: "on roads with more than one lane designated for travel in the same direction"). Divided or not. With or without traffic signals along the way, etc.
My definition of freeway (highway) is limited access, no lights, get on and go, no businesses on the side of the road, only access by entrance ramp and only exit by exit ramp. That's what I meant in my post.
Slower traffic to the right makes no sense if there are lights, left-turn lanes, etc. If I need to turn left, I get in the left lane before I need to get into the turn land. Also, slower traffic to the right makes no sense in city driving for the same reasons and where the speed limit is pretty dang slow anyway.