What audiodesign meant was that he did not care at all what people think. The correct phrase for that is obviously "could not care less" (because his care level is zero). The graphic posted by someone earlier in this thread illustrated it quite well I though.
"I could care less" is, frankly a very strange thing to say. What is the listener supposed to deduce from it? You could care less, but presumably you could care more, so it is not possible to deduce anything much about your level of caring except that it is non-zero. Why would you say that?