Something my mother often said (that her mother often said...) while I was growing up: "Always wear clean underwear! You never knew when you'll wind up at the hospital and you'd be embarrassed to show up wearing something dirty."
I have generally obeyed this edict except for once, on December 30th, 2000, when I made an exception. The underwear I took out on that day was clean, but had a small hole in the fabric at the front. There was a state-of-emergency snowstorm going on, we still had a houseful of guests leftover from the holidays and I felt like I was getting the flu, so I ignored the hole figuring I'd be stuck in the house and nobody would care. Well! Some of you will already know that I didn't wind up stuck in the house (although we were stuck in the driveway for a while); I wound up showing my holey underwear to half the state in the maternity ward because I wasn't getting the flu - I was in labor. You can bet that I won't be caught out with an extra hole in my underwear again...and I suggest you go give your own a check, too.