Not necessarily fruit, but always forbidden. The origin of this phrase stems from the book of Genesis in the Old Testament. To summarise: God created Adam. God then created Eve from Adam's rib. Once this was accomplished, God allowed them to roam free in the Garden of Eden, where they lived blissfully. They were in a state of innocence, and so were virtually immune to sin, as they had no way of knowing what it was. The only rule in the Garden was that they should never pluck the fruit from the tree of knowledge. Allegedly, Eve coerced Adam into doing just this, with the result being a fall from grace. Aware, now fully cognizant human beings, Adam and Eve recognised their indecency and so committed the first sin in history. As a result of this, by Christian theology, we are all stained with the Original Sin.

In modern terms, the phrase "Forbidden Fruit" essentially sums up a simple truth: people will always desire that which is expressly forbidden to them. Kids think that smoking is cool, married men check out other womens asses. I, for one, found myself completely incapable of not trying marijuana, on the simple basis that if all of these PSAs were harping on about it, it had to be some killer shit. I was, I must admit, disappointed by the whole affair.