[RiderOfGiraffes]

<shrug>

It's common in the USA. People I've spoken to from other countries think it makes those who use it seem ignorant. I'm providing data, not making a judgement. I know that many idioms don't make sense when dissected.

The parts of the world I have regular dealings with - excluding the USA - all say "I couldn't care less," and that actually does make sense. The people I've spoken with about this have expressed bewilderment that the alternate version should be used. They say that it doesn't make sense, and it's open to misunderstanding.

When I speak with customers I don't use the same short-hand or code phrases that I use with my colleagues. Likewise students when applying for jobs or other positions use more formal language, because to do otherwise makes them look uneducated and ignorant. I'm just saying that I've seen the same attitude towards people who use this particular phrase.

Personally, I don't care. In fact, it would be hard for me to care less. I'm just offering a datum that some might find useful.