Many years ago, I heard a sociologist tell an anecdote about being the only undergraduate at a faculty party. After a short while, he realized that somebody was watching him from a distance. Worse still, wherever he went, there his mysterious observer followed. Understandably anxious, he finally cornered one of his professors to find out what on earth was going on. "Oh, that's Erving," his professor sighed. "He's always on." The Erving in question was Erving Goffman, the author of The Presentation of Self in Everyday Life (1959).
Everyone I know who ever encountered Erving Goffmann has a similar story. The one I've heard most often is that he would arrange for his students (at UPenn, natch) to meet for class outside on the lawn in front of the library, then hide and watch, laughing at how they reacted when he didn't show.
(From The Little Professor.)