Here is the real story
From Chef Gaku Homma of Domo Restaurant in Denver.
domorestaurant dot com/qanda.html
Q. Am I supposed to rub my chopsticks together before my meal?
A. Some think that rubbing your chopsticks together before a meal is a Japanese custom meant to remove splinters. In fact, rubbing chopsticks together can encourage more splinters than it actually takes off! This ritual originates from an early Charlie Chaplin movie that was popular in Japan before WWII. In this movie, Charlie Chaplin rubs his knife and fork together as a gesture of culinary anticipation. The Japanese people who were fans of the movie at the time, mimicked this action with their chopsticks. After WWII, American GIs returning from Japan brought this American born custom home again! In Japan today it is not a commonly practiced custom.