I do my biking these days in Porland, OR... Hillsboro actually which has some of the more bike aware motor traffic. I can't exactly speak for Vietnam but I think it is fair to say that a situation in which your horn "saves you" is also a situation in which no horn would have also "saved you". Neither as a driver or as a cyclist do I ever touch my horn. In NYC and NJ I heard a LOT of horns being honked in anger... after the fact for the most part. Out here there is a lot less horn blowing going on. There are a lot fewer accidents too. Loud horns do not do anything for the accident rate. Defensive driving and riding is the only thing that really works. Just my take.

H (once an up close eyewitness to a horrific crash in Hoboken. Heard someone laying into a horn and looked up... the car doing the horn blowing took no other evasive or braking action... he plowed into the drivers side of the other car at ... maybe 20 miles an hour. The blow hurled the passenger on the other side of the car right at my feet! I'm standing on the sidewalk in stunned disbelief. I called 911 and waited till they arrived but did not wait around beyond that. I wasn't much into horns before that day.