"You guys" is the most common form of "you" plural used in the mid-west and western United States. For those who were not taught English in a region where "you guys" is standard, I can assure you that we consider "you guys" to be completely gender neutral. I can see how this phrase would seem strange to someone from a region of the United States that uses "you" or "you all" or "ya'll" or "folks", but for us it is simply a phrase that is used by both women and men when addressing a group of people of any gender (all women, all men, mixed).
See you guys tomorrow != See you men tomorrow. Are you guys done yet? != Are you boys done yet?
Now, is the etymology of the word sexist, a la "mankind"? That I do not know (it probably is), but the intent of those of us who use it is simply that it is two words meaning "you all". We do not think about injecting gender at all into the conversation, in fact we use this phrase to avoid it (as silly as that may seem)! I would imagine that this phrase is more likely to turn heads when it is used in a region of The United States where it is not the normal linguistic way of saying "you" plural.