I think you are wrong about drivers in Ho Chi Minh City (Re: issue No.85, Stop making so much NOISE!) I am a foreigner and the owner of a car in the city. I have been residing here for 10 years now and have learned the importance of using the Vietnamese honking method in traffic to serve as a friendly reminder to motorbikes that I am approaching.
I have noticed on several occasions that a failure to signal to other drivers with a honk will often cause them to veer into the automobile lane or get too close to my vehicle, without realizing that I am there. Perhaps with all the rapid economic development, inflation or high interest rates, there is simply too much on their mind to notice that they have inadvertently lost awareness of their surroundings.
My honk serves as nothing more than a friendly reminder that they are too close. Furthermore, I feel it is advantageous to use the horn to avoid legal difficulties as well, because it is not uncommon to find that collisions involving a motorbike and car will generally result in a more unpleasant outcome for the automobile driver, no matter what the circumstances.
I would like to mention that "road rage" seems to be a western phenomenon. Although there is a growing stress level to operating any type of vehicle on the streets of HCMC, I can say that aggression is not really what a foreigner visiting Vietnam should expect. Until the relevant authorities can develop a plan or a system to coordinate better traffic flow, I believe that the honk as a gentle reminder will be a part of everyday Vietnamese life.