Expressions are so common in American English that we use them constantly and don't even think about them. Some expressions, though, are sometimes said differently, depending on where a person grew up or what they heard as a child.
Take the expression, "I couldn't care less." When someone says something that you really don't care about at all, this is the expression that we use. Some people, however, say "I could care less" to mean the same thing. Are they the same?
If we take a look at them, they we would say no, they don't mean the same thing. If you tell me something that I don't care about and I respond by saying, "I could care less," it means that I still care a little bit, so there is room to not care more.
There is no doubt as to how I feel if I use the expression, "I couldn't care less" in this situation, is there?
So, when you hear people say, "I could care less," keep in mind that many people use it but it is not standard English. The correct expression is "I couldn't care less."