And the correct answer is…
Disposable chopsticks should never be rubbed against each other before use.
While waribashi, or disposable chopsticks that need to be broken apart before using, are mass produced to create a less expensive eating utensil, rubbing them together is neither necessary nor polite.
Rubbing your chopsticks together before usage tells the restaurant/chef that you believe the chopsticks to be of poor quality. It can also put into question your ability to appreciate the food you are being served.
If you notice that your chopsticks are splintery or uneven, ask for another pair rather than rubbing the sides.
