Girls are Weird...
Is there a formal body of research on why girls are so weird? Of course, that premise implies that men are the non-weird ones, which I don't think I could ever argue.
The thing that is weird about women, if there is anything, is the effect that they have on men, whether they are conscious of it or not. With a flick of the hair, a slight touch on the shoulder, a lingering glance, and all of man's rationality and sense will simply evaporate. Perhaps men have the same effect of women, but it seems to me that that they are at least moderately aware of what is happening to them -- and have at least the option to resist. Men, however, seem the hapless pawns of biology and chemistry.
Men wouldn't mind their kryptonite so much if the members of the fairer sex didn't seem so fickle, irrational, and, at times, downright crazy. But when it comes down to it, I surmise that when a woman acts crazy, it's because a man is driving her nuts. Gentlemen, you know how truly asinine we can be. Can you imagine what it's like for someone without a Y chromosome to help interpret our moronic behavior?
Since I barely understand my own mind, it makes perfect sense that women would remain an enigma. Who can fathom the feminine mind? Not I. And it's not particularly relevant anyway, since I hold the same opinion as Hobbes: "I like 'em anyway."