OP I'm not calling you a liar; but I seriously doubt that all 40 people have at any of these events made a ticket about this problem. GM rarely react to two or three tickets on one person, since it could easily be three people that just dislike this one person, and want them to be banned. Where as 40 people ticketing one person, is far more reliable and would require a useless GM to be ignored. Other then that, get someone to film when it happens, and then tell the GM that you have video evidence of what this person is doing, and how it is ruining 40 peoples fun.
If all this doesn't work, then go higher up, get Blizzards attention that one of their GMs is useless and doesn't do his job. And no, this is more then sending an angry email, letter them, call them, travel to their office and knock on the frontdoor. Seriously we here in MMOC can't help you, and we sure aren't going to solve your problem or take action on this since it isn't our problem and haven't been there on any of the events