Stop continuing to believe that the people who run conventions and companies are good people. They don't give a shit if you get sexually assaulted, as long as they can continue to do business more or less as usual.
1) Tell an executive.
2) Try not to put yourself in that situation.
3) Remember you're there to make sure attendees have a good time.
Take a moment & reflect on how absurd it is that people who run conventions, who could get sued, are still doubling down on setting him loose on their attendees.