Not yet, but I don't do much social media.

It is a shame that every disagreement online seems to degenerate into mean-spirited insults. The only thing I can suggest is that when you have a book you didn't like, that you might frame your remarks with something like "I understand why this story is important" or "I think it was very well written" before explaining why it isn't your cup of tea. Sign off with something like "It's wonderful that this book has helped so many, it's just not for me" and leave it at that.