What is the difference between hip and cool?

An interesting conversation today that tried to distinguish between being hip and being cool. One could be utterly unhip, but a very cool person. To be hip, it was argued, requires being hip to something, it means being on the cutting edge, being more current than current. Being cool on the other hand, is something else. But what else? Is it an attitude? a disposition? an image?

The claim was made that cool was relative, what is cool to one is not necessarily cool to another. This struck me as wrong. James Dean, for example, is objectively cool. Anyone who says otherwise is simply wrong. We may disagree about what is cool, but it is something we could discuss and give reasons for, this is not the case with subjective qualities like taste. If chocolate tastes better than vanilla to you, then there is no rational argument that will make you say, "Oh, I thought it tasted better, but now I realize I was wrong." But we can say, "I thought this was uncool, but now I get it, it is cool." And in this case, you were wrong in your original judgment of coolness.

What, then, is the difference between hip and cool and is cool relative? What do you think?