it just mean no

It’s an acronym standing for Can’t Remember A Fucking Thing. It’s usually used to describe embarrassment at being unable to remember someone (CRAFT moment); going onstage as the lead in the latest theatrical performance and your mind goes completely blank (CRAFT situation); the next morning after a night when you got pissed as a fart and woke up in bed cuddling a traffic cone and a string of fairy lights wound round your prick.

Nope.

Laid-back demurral, with overtones of not taking the original statement too seriously.

Can simply mean no.
Also can be used sarcastically.

i dont care.

Hell no, seriously, no!