Gamejacking is the act of pretending you're a canon part of the ARG when you're really not. People usually do this by roleplaying, acting like they're BEN or a Moon Child or something. Only fags who like to pretend they're important enough to be a part of a fictional online story do this. If you want to roleplay with the ARG as a setting, do it in the Roleplay Section, not in the other discussion boards trying to trick users.
Note: Gamejacking is not the same as roleplaying. Roleplaying is fine, in the proper sections. But users who persist that they are in fact canon and 'I'm totally ben guys lol' outside of roleplays will be labeled as gamejackers because that is annoying.