I blame anet for not having an option to report griefing, which is exactly what these people, and one in particular, is doing. He knows it messes up the event, laughs about it in map chat and does it over and over because it's allowed. This isn't a case of someone not realizing they are breaking the event, it's 100% intentional. To me, that's griefing. And there is no option to report griefing.