It never used to be like that. When I first came to Bangkok in the late 80's all you could hear was horns. It kinda reminded me of the stories of flag/latern bearers that walked in front of the first motor vehicles warning everyone of their approach. I clearly recall being in taxis and Tuk-tuks going around Silom and Sathorn and the drivers continually honking their horns everytime we overtook another car/motorcycle, passed a pedestrian, or got anywhere near anything else on the road. I used to wonder how any of it could be understood as it had become just a constant din with so many honking.
Now it seems the exact opposite, I have learned to not use my horn but just take it all in now as just another bad movie, my actions wont change that.