Very nice listing - but I challenge on "could care less" - the derived form makes perfect sense, at least in conversation - it's an ironic statement, more specifically that subset of irony known as sarcasm (where the irony is indicated by a tone of of voice that declares that the speaker means the opposite of what is being said).

Since "I couldn't care less" is generally a term used to denigrate the subject under discussion, it's sarcastic form carries more impact (sarcasm is generally held as rudeness, so is not caring for the topic). Essentially, the sarcasm reinforces the lack of concern being indicated.
Of course, in written language, sarcasm is much harder to pick up - generally authors rely on the phrase being so well known that the reader will immediately attach the sarcastic tone without it having to be pointed out. In prose the descriptive sentence usually following a character quote may contain a verb like "sneered" or "said sarcastically" but in things like letters this is harder to convey - which is why it appears not to make sense.
In short, used as an ironic or sarcastic statement the phrase "I could care less" is in in fact a more meaningful way of conveying that you couldn't care less.