One time I had the side zipper a good part of the way down for several hours before I finally caught on. I thought the dress was fitting a little odd, but I was fresh newbie then and in such in a rush that it didn't occur to me to check the zipper, and it wasn't so far down that the dress was sliding off. Plus my blouse was fitting normal against me so it wasn't as obvious as you might think. By the time I noticed, several pictures were taken of me (not by other lolitas, and it was a small local convention) and I was horrified. To this day, I have no idea how I missed that step. Later, I saw a photo of me, and you could tell in the photo. So much acute embarrassment
That same day I was having my period pretty heavy, and managed to get blood on my dress. I washed it out before I left the bathroom, but I was in the bathroom looking frantically at the dress in several angles in the mirror, close up etc. probably looking like a crazy person to make sure I got it all. Thankfully it was only a couple spots, and it was bodyline (and I have no intention of selling either, for anyone who may scared of dresses ever touching blood ever), but still.
That day was awful, lolita wise.