thefitfatty " the vast vast majority of people have done nothing but comment on the OP's original sentiment, that it's not ok for someone to comment on her weight. "
Except that was NOT her original sentiment!
Her thread is called "I'm NOT fat"
Not "DH's grandmother is rude" or "AIBU to think this comment was out of order?" or something.
But "I'm NOT fat." Followed by an opening post in which she outlined all of her stats in great detail. OP herself has said she thinks this was badly worded and she regrets phrasing it that way. However, it's not the fault of other posters, who have responded to her actual post and to her thread title, and not to an imaginary or ideal one that she didn't actually post.
On a separate issue, re BMI and health outcomes - all of the recent research showed that the original research indicating that a BMI around 25 was healthiest was very skewed by the fact that many people lose a lot of weight when they are ill and thus the lower BMIs included disproportionate number of people who were on their last legs and had recently lost weight due to serious illness.
They also included smokers, who tend to weigh less but obviously have terrible health outcomes.
Once they corrected for that by taking out everyone who died within 5 years of the study, and looking instead at that person's maximum BMI, and also taking out smokers, it turns out that the best BMI for long term health outcomes is either 20 or 22 depending on which meta-analysis you look at. I willl post the links shortly