The meanings of words can, and do, sometimes adapt over time. I would say that many people use the word when referring to someone as an idiot.
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Gervais actually said when referring to Susan Boyle, and I quote, ""She would not be where she is today if it wasn't for the fact that she looked like such a ******* mong. When she first came on the telly, I went: 'Is that a mong'? I don't mean she has Down's Syndrome, by the way. No, no! That would be offensive. That word doesn't mean that any more."
As for "Derek", I shall watch on Thursday before forming any opinions on it.