I was about run over by a couple in a truck. They were in the lane to my left, and suddenly changed into my lane. No blinker. I used the horn, but they ignored me. So, I need something that will garner attention. I'm thinking big rig horn.
As best as I could tell, the woman driving the truck that nearly sideswiped me either was ignorant of anyone being in that lane, or couldn't care less. I gave her every opportunity to correct her ways, then she ran against an abutment.
Anyway, perhaps if she had more of a heads-up...