It's kinda like saying I couldn't care less, but in a more sarcastic way as Xen said. I guess it should be 'I could care less, but not without trying hard' or some such but, frankly, I could care less.
I have no idea whether it's American usage. It's not Swiss German, that's for sure.
EDITED: 16 Nov 2009 19:35 by MR_BASTARD