A lady was aghast at my wagging finger

I wish I could have got a picture. Some lady pulls out in a way that would have caused her car to hit my very visible, very reasonably located bike, if I hadn't foreseen her pulling out without really looking, because she was clearly in an important cell phone conversation and just looked like "the type," if you hear what I'm saying. So I slowed down just enough to make it safe but not enough that she wouldn't see what she'd done, and right as she finally noticed me (a good ten feet or so after when she would have hit me) I gave her a stone-faced finger-wag accompanied by a very subtle "no" motion of the head. Her face was priceless. Agog, aghast, a mixture of ashamed and pissed and shocked. Good thing there wasn't some old lady crossing the street in front of her, because she kept going as she craned her neck around to look at this audacious finger-waggin' guy.

See, when I'm driving a car, I'm a firm believer in using the horn as a behavioral modification device. I'm a peaceful man, but if someone cuts me off, I lay on the horn in that special way that signifies FURIOUSNESS, because how else will they even know? So on a bike I have developed a repertoire ranging from the more subtle finger-wag to the "what the fuck are you doing" shrug to the screaming flip-off. I figure the next time she is at that intersection, she will think twice. And then maybe, just maybe, she will generalize it to other intersections. Maybe somewhere down the line some kid won't get run over because of MY making a total stranger feel shocked/disgusted/ashamed/aghast! I think that is called the "butterfly effect"?