I'm confused what's the difference between 'CAN hardly wait' and 'CAN'T hardly wait' ?
"Can't hardly wait" is a double negative, so it's wrong. "Can hardly wait" is correct, e.g., I can hardly wait for BIGBANG's comeback.
"Can't barely" and "can't scarcely" are also double negatives. Replace "can't" with "can." ✌
"Can't barely" and "can't scarcely" are also double negatives. Replace "can't" with "can." ✌