I'll never forget the look on Joe's face when he figured out that women have "period underwear." Joe was a co-worker of mine some years back and he bragged to me one Monday morning that his girlfriend had let him in on that little secret, as if he'd just uncovered the secret of life itself.
So for all you guys out there, I'll share it with you. Most women do have a rating system for their underwear. As our panties get a little old or out of shape, they get demoted to being the underwear you wear when Aunt Flo is in town. We wear these instead of new, fancy, or sexy ones so that if there are any mishaps, we can just toss them out. As new underwear is purchased, the rest of the panties in our dresser move down the ladder until they end up at the end of the line - on the chopping block for being period underwear and the next one to get tossed out if the slightest leak happens.
Because leaks happen.