Here are two commonly mispronounced phrases.

Correct: Can hardly wait means that I am having trouble waiting.
Incorrect: Can’t hardly wait means that I am not having trouble waiting.
Hardly means scarcely or barely and is negative. So it makes the second example a double negative and switches the meaning.

Correct: Couldn’t care less means that my caring could not be lower.
Incorrect: Could care less means that my caring is not at its lowest point.