It really shouldn't be a problem. You should be able to jump into almost any group of reasonable riders and not have any problems as long as you just concentrate on the basics, which is protect your front wheel. If the wheel ahead of you is squirrely, so what? You should never overlap the wheel ahead of you so anything he does won't affect you.

I'm so used to people pulling off the wrong way in a paceline that I always expect the worst. I just say once, "pull left or right" to the guy in front of me that is going to pull off, but I never expect them to do the right thing and prepare for an out in case they get it wrong.

The only thing I really can't deal with is people who slam the brakes on for no reason. Thats very hard to predict and hard to avoid, but I always ride a little to the left or right of the wheel in front of me, even if the wind is dead straight on, so that I can get around someone who uses their brakes.

Sounds to me like you are used to riding with the same small group of people and when you are exposed to new riders and their different styles, you are uncomfortable.