They told me that in a certain Central-American country (forgot which one it is), the middle finger is indicated in a very different way. In fact, the middle finger is not even shown.
How it's done:
You position your arm and fist as if you are showing someone your fist (aggressive sign). At the same time, you have your thumb tucked in between your middle and index fingers.
I know it's weird, but don't do it if you are visiting any hispanic country. Or else you'll get something in return.
As for the flipping the bird:
My history teacher had once told me that in the middle ages, the middle finger was once considered the POINTING finger, while the index finger is the insult finger. Is this true?
One warning to anyone from the US visiting the UK. Be careful when indicating 2 with your fingers. Given with the hand facing the wrong way it might get you into trouble - or at least some very strange looks.
I would care less. My best excuse is that I'm not from their country and some of their rules don't apply to me.
j/k
