The following list, which is in no particular order, contains a wide range of behaviors that an author shouldn't have to face in my opinion. Some are downright hateful (Internet Trolls, Goodreads Bullies) and others are just rude or unprofessional.
I campaigned once to vote down a review, but I was questioning the value of the review, not the book itself. And definitely not the author. In other words, I was exposing bad behavior, not spreading it.