这句话的意思是“我不在乎”，“缺乏兴趣（lack of interest）”，也就是：I don't care at all. 或 I don't give a hoot.

例如：人家如果问： What do you think of the budget-cut?（你对预算削减有何看法？）

你回答： I couldn't care less.（我毫不在乎）

How do you like Mr. Lee's political point of view?（你喜欢李先生的政见吗？）

I couldn't care less.（我才不在乎呢！）

但是有时说话者也可能口是心非： 例如：

I couldn't care less about the promotion or pay raise.（我不在乎升级或加薪）

而实际上他是根本在乎升级和加薪的，那么人家也许就会回答说： Yes, you do（care）.

至于 I couldn't care more. 就是“我很在乎”（I care a lot.）或 I care deeply. 同理：

I couldn't agree more. = I totally agree.（我完全同意）

I couldn't please you more. = I did my best to please you.（我尽量使你高兴）

I couldn't be more right. = I am totally right.

但是老外为了自尊，不愿强调自己的错误，所以很少人说： I couldn't be more wrong. 注意：一般人都用否定句，但也有老外把肯定句与否定句互用。

不过，严格来说，I could care less. = I care to some degree.（care 的程度可能减少） I could care more. = I care some.（care的程度也许增加）（主词可用任何人称代名词：he, she, you, we, they 等。但只用 could，不用 can。）