as this is new to me, i defer to others about the historical progression of this discussion. however, please do not paint all americans with one brush. i'm an american and i have always used the phrase "couldn't care less." i am 51 years old and have never, to my recollection, heard the phrase any other way until recently, when my teenage daughters took it upon themselves to correct me. i was taken aback that they scolded me for using what seemed to me a perfectly logical phrase. and i had no idea that i had stumbled over the tip of a grammatical iceburg. also, this notion that "could care less" is a form of sarcasm seems a bit of a red herring. sarcasm is most powerful when the pendulum swings fully in the opposite direction. "could care less" hardly meets that criteria without substantial modification. (and yes, my almost exclusive use of small case letters is intentional, but unrelated to the topic at hand.)