The story that's common over here is that it was the first and second finger the French threatened to cut off, which is why we traditionally wave two fingers. I've heard the theory pooh-poohed on the grounds that you use the second and third fingers to draw a bowstring; I wouldn't know, but just try waving 2 & 3 instead of 1 & 2 and see where you get. And pardon my French(!), but I'm sure the expression the Goddams shouted would have been "Fuck you!".

It's interesting to note, while we're on the subject, that the Western gesture for "OK", forming a ring with the thumb and a finger, means "arsehole" ("asshole") in some Eastern parts. Don't say I didn't warn you.

Steve