Sometimes women turn into some type of mythical beast.
It's best to avoid them during this transformation..
Don't ever tell a girl she's PMSing though, it's never polite. =)
Just let the mythical beast be, and within a few days you'll get your girl back. ;)
Person 1: My wife is turning into a mythical beast!
Person 2: She's PMSing, my friend.
Person 1: Here she comes!
Mythical beast: What are you doing on UrbanDictionary.Com?!?! Don't you love ME?! Get over here, NOW!
Person 1: I got to go. =(