I know what you are talking about, it's happened to me too. I also have shorts that fit fine, a great saddle and use plenty of chamois cream. I have always wondered if it wasn't due to the temperature difference of my skin (really hot) and the shower water (lukewarm usually for me) - because it only happens in the summer time. Usually I just try to wash down there as thoroughly and quickly as possible and bite my lip and it goes away eventually. Haven't died yet