There is an unspoken rule of the office restroom, which I believe is not limited to my own office building. When someone enters the restroom and one of the stalls is occupied and silent, this typically means the occupant is waiting for the intruder to leave before continuing with, um, her issues. The intruder therefore understands that she needs to finish her activities quickly or submit a silent challenge to the original occupant, the message being, "I don't care how tight your buns are. I'm waiting you out." Then, a period of stressed silence ensues, broken only by a goading warning cough or an "ahem" retort before someone flushes, thus throwing in her white towel, (or toilet tissue) and leaves the restroom...so the winner can proceed with her, you know, victory ceremony.