From the DAILY CALIFORNIAN
Think about the literal meanings of the phrases. If I can’t care less about something, then I must not care about it at all. My level of caring is at a solid zero, so it’s impossible for me to care any less — there is no level below zero. Therefore, this phrase can be used to sassily express that idea that what you’ve just told me is pointless and that spending any time thinking about it would be a complete waste of my life.
On the other hand, if I can care less about something, then I must care about it at least a little. As a matter of fact, it’s a very open-ended statement. On a scale from zero to 10, my amount of caring could technically be anywhere between one and 10. Either way, it is possible for me to care less.
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