When I first heard the word "unobtanium" used in Avatar it broke the 4th wall for me because I had heard it in other contexts, generally used in a joking way and so it seemed really out of place.
Was it meant to be a joke within the context of the story? It seemed to me that the characters used the term literally without any sense of irony, as though it were the accurate technical nomenclature for the mineral. But that doesn't mean it actually was the true name; it could have originated among the characters as a joke but then become the de facto jargon of the humans on Pandora.
Or was this just a badly placed in-joke that most audiences were expected to overlook? Some other reason?
Is there any known explanation either within the story or background of the film?