I always have horrible mood swings when on my period. Lately they've gotten SO much worse, and I really do take most of them out on my boy. It's not that I mean to, it's just that I get in this weird mindset where I snap at everyone, and when people get emotional who do they turn to? Their significant others. So, of course, it's expected for him to care, and let me be a ***** to him. And when he won't take it{why should he?!}, I snap even more. We have our fights, and then drop it, because we both know I didn't mean it. Of course I have to make it up to him later, as I should, but it's understood to not take it personally.

If the fights are really emotional, from her point of view, but not emotional at all to you, then that's a sign of PMS. Also if she just snaps out of nowhere and won't explain why, or is trying to make you feel bad intentionally.