Or in the case of "you guys", the mistake is perfectly clear, but it's 1) in no way intended to be sexist and 2) deeply ingrained in the culture I grew up in. I can understand why someone might object, but the fact is it is the standard gender-neutral second person plural pronoun around here. If my wife was going into town with her best friend, I would not hesitate to ask her "How long will you guys be gone?" nor would she give me an odd look if I did.

I can easily imagine people making a fuss about this leading to a state of near constant self-monitoring, and I'd probably get excited and slip up on a regular basis...