THEATRICAL BAD LUCK #1
Actors and stagehands alike believe whistling or clapping backstage to be bad luck. This may derive from the time when sailors operated the scenery, since they were handy with knots. The sailors communicated with one another by a system of whistles and claps that, if inadvertently used by an actor, might result in scenery falling on their head.
Wishing an actor good luck is unlucky, since folklore tells that to fool evil spirits, actors should request the very opposite of what they want--hence the phrase "Break a leg."
Wearing green is considered unwise in any theater, since green is the fairies' favorite color, and to wear it will provoke their jealousy and ire.
P.G. Wodehouse (1881-1975)