She was a school teacher

A gentleman was much surprised when the good-looking young lady greeted him by saying, "Good evening." He could not remember ever having seen her before.

She evidently realized that she had made a mistake, for she apologized, and explained:

"Oh, I'm so sorry. When I first saw you I thought you were the father of two of my children."

She walked on while the man stared after her. She did not realize, of course, that he was unaware of the fact that she was a school teacher.