Hmmmm, interesting point. The slightest implications of each word (in/on/with) is definitely conveyed between me and my friends >>which poses the question: is that supposed to be (my friends and I)?

If I were to say "I could care less" I would mean that I probably could care less if I wished to, but that is beyond my caring-to-do to do it. In other words, as IngishKahn said, sarcasm.

The word shrew does carry a negative connotation that originated in Olde and Middle English. In Middle English, the world "schrewed" meant to curse. The original definition is evil, bad, wicked, mischievous, schrewish (?). In contemporary English, schrewd implies a keenness of mind, sharp insight, and a cleverness in practical matters which in my mind molds a mental image of a cleverly cunningly conniving kind of person.

For anyone who cares to read on, here are a few synonyms that might find more use in certain circumstances~

Sagacious - implies keen discernment and farsighted judgment, as in a sagacious counselor

Perspicacious - suggests the penetrating mental vision or dscernment that enables one clearly to see and understand what is obscure, hidden, as in someone with a perspicacious judge of character

Astute - implies shrewness combined with sagacity and sometimes connotes, in addition, artfulness or cunning, as in an astupid... er i mean astute politician