The unforgivable sin is sinning against the holy spirit, not grieving the holy spirit. However, I cannot cite scriptural references right now.
I was told when I first became a JW about someone who was an ex-JW and had written an "apostate" book. I was told by an elder in our congregation that this person / author had committed the unforgivable sin, had sinned against the holy spirit, and could never be accepted back into the organization (as if he would want to be accepted back!).
The subject came up another time. In 1969 at a large assembly there was a drama about a bunch of JW weirdos, a wife named Clara whose husband left her, a kid named Buzz Sawyer (like the comic strip character) who robbed a gas station, and a girl who got really p***ed off at the whole bunch and walked away from the "truth."
The latter character / girl (whose stage name I can't recall) actually uttered the words "me, a mere woman?" in a very sarcastic tone. It was stated at a meeting that this character / girl had committed the unforgivable sin.
When I looked at the scriptures about the unforgivable sin, it appeared to be talking about a sociopath, or someone who does not care that what he or she does is wrong or "sinful" or hurtful to him/herself or others, i.e., "unrepentant," with no desire to change.
Seize the day, and put the least possible trust in tomorrow. - Horace
I have learned to live each day as it comes and not to borrow trouble by dreading tomorrow. - Dorothy Dix