That maybe so but common usage isn't aligned with what the Highway Code defines as correct usage.

Take lights for example:

+ flashing headlights on a dual carriageway or motorway is a way of telling a driver to pull across so they can pass

+ flashing headlights near an obstruction is a way of telling another driver that you're giving them priority

+ following on from the previous point, flashing back is a way of saying thank you to the other driver for letting you take priority (this is done after you've already started moving to make it clear that you're not trying to hand priority back)

+ flashing hazards briefly is also used to say thank you, albeit typically if a vehicle is behind you rather than in front

+ flashing hazards on a duel carriageway or motorway is a way of warning other drivers that you're breaking heavily (as break lights don't inform the spectrum of difference between soft breaking and emergency stops). At least in this scenario you are actually informing others of an oncoming hazard

I'm sure there'll be other colloquialism I've forgotten too