Please don't start carrying weapons.

Granted, I am a peacenik Canadian. However, should the trend catch on, we'll get a reputation similar to (and perhaps worse than) the kids who throw sticks into your spokes -- cagers will think we're out to ruin people's days and treat us similarly.

Remember, you always have a bike between you and a threat. Non-violent resistance like parking in front of a person for a minute or so has worked for me in the past. When the person got out, the societal implications of stopping traffic like that made the people behind him really dislike him and begin to honk. He threatened to start a fight, so I made sure that every car behind him (whether they disliked me or not) knew this fact rather loudly.

Sometimes the best offense is really a good defense.

I'm not sure what I'd do if confronted with a violent attacker. I mean, I have a bike I can lift and use as a weapon if I have no other option. And a U-lock. Fortunately, violent outrages seem to be a rare occurrence on the roads here.

Edit: Just to add, make sure you pick your battles wisely if you do decide to confront a driver. Have a workable escape plan just in case. For example, confronting a driver on a busy street with many alleys and cross-streets is more likely to get you out of there ASAP if he or she turns out to be violent.