I don't condone it, unless it's discussed beforehand.
Make sure that the rules are known ahead of time, or don't do PUGs. It's that simple. People will get a reputation, and that will take care of it. Let them screw themselves by being a jerk.
Also, it's always helpful to have some sort of a voice chat server when you're doing groups like this. Makes communication in those situations a WHOLE lot easier.