Hope that doesn't happen to me :P I have really low tolerance for rude people, so that would definitely not go down well. I love these conventions though - like we're talking but then someone else shows up and you kinda have to talk to them too and we sit there, listening to what the third person says and glancing at each other awkwardly - it's like this mutual understanding like we're on the same team. It's nice.
That being said, when someone is rude, I just black out, you know? I'm like okay buh-bye, so yeah, definitely not a good idea :))
When this happened to me today I simply just walked out and left the two other's to their bullshit. I have a low-tolerance to rudeness...Hell, to people in general. :)
That's because a lot of people are rude :P