Ime, tailgating is sadly common in my part of rural France. To the point where I think it's taught!
In truth, I've no idea why it happens but it seems as though confident & safe overtaking is either not taught or perhaps more realistically rarely practised, due perhaps to fewer cars on the road. (Btw, I agree with GrasB's excellent explanation ^^^ of a good, safe overtake)
Whatever the reason, it's not an unusual occurrence to have a car steam up behind you and just sit there.... and you'll be the only 2 cars on the road for miles! They'll invariably hang out slightly to the left of you too, sometimes with the drivers side wheels in the opposite carriageway. They clearly want to overtake (or have you dematerialise preferably!) but lack either the space, or the courage or ability to do so. So they'll just sit there, on your bumper, for miles.
What makes me believe it could be lack of overtaking training is that you'll see it behind slower and bigger vehicles too. Cars often stick themselves right up the arse of a truck, no possible way to see past it and then proceed to do this almost comical swerving out into the opposite lane to see if it's clear! If they'd only hang back a couple of hundred metres, they could see when it's clear and then commit themselves to a good overtake.
Re flicking the brakes (for brake lights), this is something I actually do when I'm on my motorcycle if, for instance, there's something up my arse when I'm approaching a town. Reason being that I usually slow down on engine braking rather than the brakes, so flicking the brakes only alerts the tailgater to the fact I'm going to slow down... and quite quickly too, in comparison to a car anyway. I don't do it to annoy or irritate a tailgater.... besides, chances are that they're not paying too much attention anyway!
