Cinema Retro http://www.learnaboutmovieposters.com/newsite/LAGNIAPPE/CinemaRetro/CinemaRetro.asp always comes up with interesting stories. Here's a quote from a piece about stand up comics who plagiarize (they cite the New York Post as source material).
As any stand-up comedian will tell you, comedy is serious business. Comics have an unwritten code of honor that states "Thou Shalt Not Steal Another Comedian's Joke". . Among the next generation of comedians, however, the practice is akin to an author committing plagiarism...In the new book Comedy at the Edge, author Richard Zoglin interviews prominent comedians who were allegedly ripped off by their equally prominent peers. Comic David Brenner recalls being so infuriated with Robin Williams "sampling" some of his best lines that he threatened the beloved funnyman with bodily harm. Radar magazine recently ran an in-depth article on this phenomenon and found that Williams' presence in the audience of a comedy club often necessitated a warning signal to the comedian on stage to refrain from using any lines he did not want to hear coming out of Williams' mouth in the weeks to come. Williams must be out of the habit of visiting such clubs in recent years as evidenced by the response to his latest "comedies".