In North America it is Against the law. Or atleast in the USA it is for sure. The slowest moving traffic MUST move to the right lane. The left lanes are for passing. If you like I can get you a driving manual.

And no people generally do not come flying up behind you flashing their lights because most people know the rules and follow them. When they see a vehicle coming up behind them the move over to the next right lane without flashing being required.

And BTW even if you are going 80 in the left lane and the maximum speed is 70 and a faster vehicle comes up behind you, you are required to move to the right and let him pass.

Hmmm it seems you are stating assumptions rather than actual laws and this is a huge part of the problem here - everyone assumes their way is correct and the other persons is wrong regardless of the actual rules or laws.
_______________________________________________________

"A Wise Man knows what he does not know!"