I attended my first s-f con in 2003, when I was 46. During one of the panels, I noticed one of the authors kept refilling his water glass from under the table - despite the fact the water pitcher was ON the table.
Innocent me. I soon realized he was keeping a bottle of vodka under the table.
I once moderated a panel where one member - who was admittedly very knowledgeable about the subject - refused to yield the floor and was so enthusiastic that everyone, panelists and audience alike, had to let him hold forth for the full hour.
I mean, short of mugging him and stuffing him in a barrel, it was obvious we would not be able to shut him up.
One time I was on a panel where a few of the other panelists were good friends with each other. They chatted among themselves and pretty much forgot I was there at the end of the table. After a while I realized I wasn't going to be able to participate, and I slipped off and into the audience where I could relax.
It took them ten minutes to realize I was even gone.
One time I was moderating a panel when, from next door, another moderator came in - saying that his panel has poor attendance - and said that we should combine the two unrelated panels, which he then did on his own without waiting for anyone's feedback.
This was a literal hijack of my panel, and it was pretty astounding. I was dumbfounded at the size of the ego of the douchebag. He essentially wasn't satisfied with the size of his audience, so he stole mine.
I was in the audience for a panel where the moderator tried to keep all the panelists - as well as the audience - engaged. One author, thinking that he had cut her off at one point, therefore went on strike and thereafter, every time he tried he tried to draw her back into the discussion, would only say, in a huff, "I like bunnies."
So yeah, a lot of crazy crap happens at conventions. But in all the cases I just mentioned, nobody was expelled from the con.