1.) For one, of course, the fact that a woman can be "the Man" might not be self-evident. But, of course, a woman can.
2.) Secondly, how would our understanding of this phrase change if it was, instead, "She's the Woman!" or, perhaps more interestingly, "He's the Woman!"? If you think that sexism is dead, consider this last question fairfully. Any and all answers are welcome, of course, from all three of my readers.
3.) Thirdly, I found it interesting that someone a bit older than average would use this expression. Now, this somewhat-older-than-average coworker is generally quite with-it, and I think that this is particularly true linguistically. (This, unlike some people, whose aquisition of slang seems to have stopped when they were in their 20s, whatever decade that was.) But I still found it interesting, and wondered when that expression became common. Anyone know? Or have access to a reliable idiomatic dictionary?
I replied, "we are the Man"
Anna said "and the Woman!"
Anna is British, so the idiom "the Man" may not be as internal for her as it is for me, but I thought that was interesting...
I think that "the Man" has two identities - one is positive, and conveys success, while the other is negative, and conveys opression.
So given that there are both positive and negative meanings, I don't see it as a sexist issue - more of a "the way slang developed" issue. But hey, I could be wrong...