Within Chaotic Fiction, there are only a few rules, one of which is that in each person's story, their own blog is canon, and all others may not be accepted as such. When a player forcefully tries to force their way into blogger's story, it changes the dynamic of the story. In otherwords, the intruder has tried to hijack the blog for their own purposes.
Notable gamejacks include uses of Wiffin or Periwinkle, Powers, self intrusion, forced Retcons, and playing as a pretentious know-it-all that knows more about the Slender Man than the oldest blogs out there. This also includes 'giving tips to kill Slender Man, aside from wild guesses', 'claiming to give bloggers items' or anything else that removes control of the blog away from the writer.