I've often fantasized of having some sort of pole, sticking out from the bike parallel to the road and into the road at around rear wheel height (would fit onto a rack nicely). The pole would have a diamond tip, as well as being spring loaded. The idea would be if a car came too close, it wouldn't knock you off the bike, but would cause a nice scratch on the car. Any argument of whether or not a car came too close to you could be easily negated as if the car hit the flag, they were too close and you could clearly indicate how close someone came to you!!! Now of course, I wouldn't really do this (very tempting though it might be), but it got me wondering, I've seen people in the past cycle with a similar arrangement (assuming there was no tip at the end, just a small triangular neon orange flag). Anyone had experience of this? Did it help? I'm assuming for city commuting this wouldn't be practical, but I reckon it would be perfrect for my commute. Just curious for any feedback.