I freeze, I stammer. You want to make sure we hang onto the context here. A situation like a convention may feel social but it's still business. Remembering where you are and what that context is will help. And here are some specific points.
Some people just have to have the last word.
You want to tell them to shut up. They have to have not only the last word but also the cleverest line, the funniest joke and the most exhilarating story. Don't be this person. Another type you'll run into is the person who can never let a subject go. Over and over and over he brings it up, rehashes it, talks it to death.