My normal group was there, and then like 10 other people. Everyone had brought a friend and they had all brought friends, and some people had just shown up because they wanted to play. And for some reason I was still trying to run the same adventure that I have planned for our next session. So I spent a long time trying to talk over everyone and tell the normal group that they had arrived in town. And then I shouted out "Alright! The rest of you are in town" at which point one person speaks up and goes "umm... how do I memorize spells?"
I woke up in a cold sweat :p