As a cyclist in that situation I will sit up straight, follow a straight line, slow a bit and wave the car on by. That way I am controlling the situation more.
If I am a driver and the situation is getting out of control behind me, I will tap the horn to try to make the cyclist know I will pass WHEN it is as safe as possible for me, the cyclist, and cars behind me. I try not to drag things out too long as I know drivers behind might swerve to the right to see around and inadvertently hit the cyclist.