I could care less about trigonometry.
Okay, we hear it quite often, but it should be "I couldn't care less," not "I could care less."
The former indicates an apathy than cannot be exceeded. The latter, however, expresses a certain level of caring by plainly stating that the one could care less than he or she does, but the person does indeed care.
So, on a scale of 0 to 10, their caring is somewhere above a 0 (zero). That person's caring may be at a 4 or 5 or a 2 or even a 1. But, the person still cares, unlike the person who couldn't care less. That person is at the lowest point possible on the caring meter.
In other words, the vast majority of people misuse the expression and wind up stating the opposite of what they'd like to communicate.
I know it's hip to be apathetic, but please don't be so apathetic that you're apathetic about the proper use of expressions of apathy.