I don't believe 200's ever ruined my night. I've had nights where I've had to get a bit squelch happy or detuned it not long after logging in, but such is the way of things.
When I know I'm in for a long night is if I notice my gunnery isn't where it normally is. I'm not a blindingly great gunner, but there are shots I am confident in, and if I start off the evening and blow a couple of easy shots for no good reason, I know it's probably going to be a struggle.
Wiley.