learn the rule

could care less

If you don't care about something at all, the phrase you want is:

I couldn't care less.

This makes sense. Your level of caring is at zero. There is no lower level you could descend to. You couldn't care less.

The version many people say is:

I could care less.

This means the opposite. If you could care less, you currently care at some non-zero level, and a lower level is possible. It logically implies that you do care.

The phrase needs the "not". Without it, you're saying you have room to care less, which is rarely what you mean.

If you say "I could care less" about your spelling, then by your own admission, you care about your spelling at some level above zero. You also still look stupid.

Think of it as a meter from zero to ten. "Couldn't care less" means you're at zero. "Could care less" means you're somewhere above zero. Pick the one you mean.

I couldn't care less whether you get this right. Honestly. Couldn't. Care. Less. Try it.