If the phrase "toxic fandom" has been thrown around I've totally missed it. All I was thinking about was that for the last Ghostbusters movie, people started hating on it before the trailer even came out, back when we found out there would be women in it. The same element was at play -- with totally different people, mind you -- when people were complaining about ScarJo in the Ghost in the Shell movie. I have no idea how other people use that term, if they even do. But to me, it's when the fandom is so obsessed with some form of purity that the work is never given a chance. The prejudice is the toxic part, along with inciting others to share that prejudice.
"Kitto daijoubu da yo." - Sakura Kinomoto