Sridhar Srinivasan asks about an amazon.com review (emphasis added):
"…After seeing the reviews, I bought this book in new condition at a really cheap price. I couldn't be less satisfied. The book explains all details in clear detail, so that even talented high school students could understand the text. The images that accompany the text greatly reinforce the main ideas…. "
Sridhar observes that the author seems to mean "I couldn't be more satisfied", and wondered whether there's any connection between this and the idiom "I could care less", used to mean "I couldn't care less".
On the face of it, the two cases look very different. The phrase "could care less" has 4,780,000 Google hits, while "couldn't be less satisfied" has only 10. And the other nine out of ten cases are used to refer to the lowest possible level of satisfaction (e.g. "I couldn't be less satisfied without slipping into a deep depression.").
In the case of "could care less", the apparently reversed meaning has triumphed for many people, becoming simply an idiomatic way of indicating lack of concern. And there's a plausible general mechanism for the development: "negation by association".
In contrast, the reversal of meaning in "couldn't be less satisfied" was apparently an isolated slip of the brain. Such reversals are common when negations and scalar predicates are combined, as in "Don't fail to miss this spectacular event" or "No head injury is too trivial to ignore".
This particular instance of that general type of slip is less probable than many others, since there is only one negation and one scalar element involved. Still, the general psychological mechanism is probably the same.