I’ve only been driving in the U.K. for a few years and when I lived overseas everyone followed the strict rules.
The U.K. is different and one thing that annoys me is when you are pulling out of a side road and people flash you to pull out in front of them.
Firstly, if I miss read the flashing of lights/hand gesture and crash into them, it’s my fault.
Secondly, the car behind them can’t see what they are doing and could hit them. There is the chance my car could get his by this impact. I could also be the driver behind and no pay attention for a split second and crash into them.
Thirdly, it’s often pointless and not doing a good turn. For example today I wanted to turn right and a car was driving from my left. He flashed me to come out and there was an empty road (just one car behind them). How is it beneficial to me to save a few second but also maybe cause a crash.