An elderly lady came to see a young male doctor with her husband. After the consultation was finished, the elderly man suddenly asked the doctor for a piece of paper and a pen. Although a strange request, he complied, and the man quickly wrote something, then handed the folded piece of paper to the doctor. He told him to read it as soon as they had left.
The doctor thought that the man perhaps had an embarrassing medical complaint he didn't want to talk about in front of his wife, so the doctor didn't hesitate in obeying the request. Once the couple had left the room, the doctor sat down and read the piece of paper.
Its contents were thus: "Your fly is undone."