Every conference since forever has maintained a "that person is an asshole, they aren't allowed to attend" list. Prior to COCs the list was unofficial, the rul

Every conference since forever has maintained a "that person is an asshole, they aren't allowed to attend" list. Prior to COCs the list was unofficial, the rules unwritten, and often the rejection masked (sorry "sold out" in the days before the internet so less likely you'd find out that was not true... or just drop your signup form & check in the shredder). There's no way to prove anything. It's DEFCON, not a court of law. The organizers can refuse anyone for any reason. Either you trust them to make good decisions for the benefit of the conference and attendees... or you don't.