For example:
Currently I'm thinking about the Mini but think it might not be pocketable enough. So I care about it.
If I buy it and decide it's not pocketable enough then it is out of the running and I won't care about it at all.
Therefore I currently can care less about the Mini than I currently do which makes it correct to say I could care less about it. Saying I could not care less is incorrect at this time because it implies that its impossible for me to care less about the Mini than I currently do, which as I've shown is incorrect.
Now if I later decide I don't want the Mini, it would be correct to say I couldn't care less about it because I then wouldn't care about it at all. Which is not true currently.
Don't get upset about your #GrammarNaziFail.