A car pulled out onto a roundabout one early morning and nearly hit me. She ended up in front of me and I gave her the finger! Having done that I realised that I didn't feel any better for doing it, I felt a bit stupid really. And, to cap it all, she didn't see me. What a waste of time.
I have now tried to perfect a look where I look on them in pity and give a little shake of my head. It works in most situations whether I am driving a works lorry, car or on a cycle. I copied it from my wife who looks at me the same way.