This happened substantially before my time, but as the library employee involved was my mother, I tend to believe it.

A female patron came to the circulation desk and said that when she let them know, they should call the police. She gave no more information at that time. It seems that a male patron had been exposing himself through the narrow opening between their study carrels. Sure enough later that afternoon, she announced "it's time, oh and maybe an ambulance too!"

Upon investigation, we found out that she had waited for the exposure and smacked the exposed part with her hardbound Webster's Dictionary. The paramedics revived the unconscious male and the police cited him as well.

Hopefully he was cured of this particular vice.