So, if the response from the conference director was that they should never have allowed the guy to come then it sounds like he was a known quantity in this reg

So, if the response from the conference director was that they should never have allowed the guy to come then it sounds like he was a known quantity in this regard. When I've run conventions there has always been a note that the committee reserved the right to reject anybody's membership and did not have to give a reason. We've never had to use this but we've always had it as the nuclear option and had one person who we were ready to use it on. If the person is already at the conference then you may need an acceptable behaviour policy that allows you to act, and you need it to be worded such that it applies to all conference attendees for the duration of the conference regardless of whether they are in conference facilities at the time. It's also best if it is short and broad, it's very easy to spot acceptable behaviour policies that have grown in response to specific events, and they are deeply discouraging when viewed by newcomers and outsiders.