Here's an Oz answer! When I was a child a thousand years ago the single finger didn't seem to be used - the 'backwards peace sign' was, and it was regarded as being very very rude. In the early 70's the middle finger flip came in and was often accompanied by the phrase "sit on that and spin". (An interesting, if anatomically difficult, thought.)
These days it seems to be used a lot to the driver who cuts in front of one when 2 lanes merge. One has been known to flip the finger discreetly below window level - the aforesaid driver is usually male and large, and I am female and small.......and not stupid.
Cheers
JennieG