Welcome to the forum! Unfortunate that it was close calls that brought you here rather than running into a super nice forum member on a trail or something.
I have found that the nicer I can manage to be, the more headway i seem to make with drivers behaving badly. You probably know that this is difficult when someone has deposited a giant metal box in your lap.
Also, please note that I’m pretty sure a 140 dB horn on a bicycle is actually illegal in DC, though it’s unlikely anyone is going to cite you for it unless you blow it at a police officer.