I never do it (regardless of gender) simply because it riles people up to the extent that (in my experience alone) it never makes things better. Possibly a machismo thing as guys in cars react badly to a bloke doing it? Anyway, had a van driver threaten to break my arm and a Saxo driver swerve at me deliberately the only two times I've done it (purely instinctively).
As with Greenroofer I find the cam helps, no need to get into an altercation, can check the footage later. Occasionally there's something so stupid I find I have to shout, but fortunately (and this is casting no aspersions on anyone not so programmed!) I've never been much of a swearer and generally resort to 'Idiot!' or a sarcastic 'Well that got you far!' or 'Indicate!', and a few times, 'I'm Still Here!' as I get squeezed to the side).
@Min, you're not a girl, you're a lady ;)