In what countries is it offensive to make the thumbs-up sign?

In much of the world today, the thumbs up means, "O.K.", "Yes", or "I approve." But in Iran, Afghanistan, and parts of Italy and Greece it is an obscene insult, especially when combined with a sweep of the arms. It these places it roughly means, "Sit on my phallus," and carries the same stigmatism as the middle finger. In southern Sardinia, where this gestures is noted for being particularly obscene, a hitchhiker would be well advised not to wave his thumb in the air expecting a car to pick him up, or he may find himself under the wheels of a large truck.