haha, that's the way to do it
On the finger topic, I routinely use the middle finger to say "hello" to children and the elderly. It is my custom. So I do not understand the hostility.
[sarcasm yes]
Now for the OP question, though I commute by bike every day, very luckily I have not had an altercation in months. Howeva, In former incidents I've been consistent even despite being angry or shocked. All I do is the "What?" arm expression. Just one hand off the bars, palm up:
I don't
normally wear SWAT gear while cycling. This is just an example.
On one occasion when someone yelled at me I did the "What?" signal, but then caught up to them and used my phone to take a picture of their plates, like Alienator mentioned. I think filming or picture taking is the best recourse. You can see what they did and what
you did and decide if the Police need to get involved. But the fewer incidents the better. I take pride in riding in places that stereotypically hate cyclists but minimizing incidents.
One occasion I'm not proud of involved the finger, because I made the
choice to use it. I was riding on a four-lane road with no shoulder, staying as right as was safe, and a woman passed close next to me in a van and started yelling at me, windows up of course. Uh, I can't hear you. At first I said, "what?" but she just kept yelling, so I decided to throw the finger. Nothing came of it, but like has been talked about here, that is a dangerous move. No one is justified in reacting poorly to the finger and seeing the finger is a poor excuse to lose control, but the type of person who would yell at a cyclist could easily become the type to swirve right and take me out like Euro car versus Juan Flecha. Anger and
fight or flight might be hardwired, but responses like the finger are cultural. It's a choice, and there's no discussions on the road unless you catch up at the next light.