Renton – have to admit over the last 25+ years of driving motorbikes and cars that I have undertook more than once, but it does lead to the situation you found yourself in more often than is acceptable. So now I'm older and wiser I dont do it anymore and thats from experience, better to bide your time.
I will also share with you a true story which happened to me about one year ago.
I was driving south on the M74 a night on a Sunday with all the family on board (in a BMW saloon btw!), the motorway was very empty as it was late evening. There was a large pick up truck with a crew cab cruising down the outside lane at about 60mph. After a while I gave him a polite short single flash to remind him of correct procedure to pull over to inside lane.
He immediately rammed on his brakes and whilst swerving all over the road he eventually stopped in the middle of the two lane motorway on a sweeping right hand turn!! I am now stopped behind him after an emergency stop on a turn, on a motorway, at night, with my wife and kids in the car. He then engages reverse and the window at the back starts to wind down. There was enough space between him and the crash barrier for me to get out of a potentially hostile and dangerous situation, which I did instantly.
All that from a "friendly" flash, and no speeding or tailgaiting..very scary. I didnt have time to get his number needless to say.
Its not worth it.
I have since changed what was a inconspicous dark blue beemer to a bright red one (bought it for the diesel engine not the colour) with tinted windows and its very noticeable how much people cut you up just because of the car.