! prevents it from kicking you and @ makes it only work if you are an op.
Just to clarify this statement for those who might wonder about it... ! doesn't really prevent it from kicking you. What it does is prevent that event from being triggered by you (so it won't trigger if you're the one joining the channel).
Actually, you don't even need the ! now that I think of it... you wouldn't have @ status if you're the one joining the channel. So you can remove the ! and it will still work.
