I would include "I could care less" instead of "I couldn't care less" but I know there's some debate about that one.
What debate could there possibly be about those two phrases? Maybe like misunderstanding what the words mean?
From those two statements, one means you do care and could care less if you wanted to and one means you couldn't care less even if you tried to.
One of my favorite misinterpretations of words is not understanding contractions and thinking a contraction like "should've" means "should of". Of course, this simply comes from complete ignorance of the English language and/or not paying a lick of attention while in school.
Then there's "ITS" vs. "IT'S". The misuse of these two words just slays me. And then there's the misuse of "THEN" vs. "THAN". It seems very few truly understand there is a difference between the comparison word---THAN---and the word that represents time/even sequences---THEN.
For example, the proper use of than-----
"I'd rather have a bottle in front of me THAN a frontal lobotomy."
The proper use of then-----
"We ate dinner THEN went to a movie."
Not hard or exactly rocket science, but most seem not to understand the difference.