The worst for me is when people say "I could care less."
Do you even think about that sentence before you say it? How does it, in any way, convey what you are attempting to communicate?
Let's break it down:
"I could care less." That would indicate that you are not yet at minimum caring capacity, and I should therefore continue, on the basis that you still contain some care for the topic.
The saying is "I couldn't care less." Drill that into your brain and don't forget it.
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On a sidenote, I've recently noticed I have a disturbing tendency to say, "Worst-case scenario:" I have little doubt that my peers think this to be annoying. I'm making an effort, I promise.