on a more serious, general note, i would advocate against anything built into the car that uses the computer to mess with other drivers in any way. for one thing, it's just kinda stooping to someone else's level to "get them back." i think what happened to me is funny, but i just don't do stuff like that anymore because it exacerbates road rage, both in me and other drivers, and if everyone was driving offensively instead of defensively, the roads wouldn't be safe for anyone.
also, to incorporate the carputer into the execution of such fruitless revenge tactics reduces the legitimacy of the carputer itself, in my opinion. what i'm saying is, i think we're all researching and developing a useful and soon to be necessary tool, and while "cool" is always top priority, we shouldn't get caught up trying to implement anything that doesn't really benefit us...and other than releasing a little anger, where does yelling at the guy behind you get you?
that's just my $0.02...and on that note, it's your car and you can try out whatever you want on it.