When you encounter a raging cager instead of flipping them off, it is so much more effective to smile and wave. Here's why:
1) Often they become so confused by your non-response that the tirade stops and they wander off.
2) If they're screaming at you to get a reaction they just failed. You win!
3) Should things escalate further and the law becomes involved (they never have for me thank goodness!) you are altogether in the right and you can rightly claim that you in no way provoked them.
For the very special cases, I sometimes blow a kiss.