What the gesture can imply
After snapping apart disposable chopsticks, some diners rub the two halves together to knock off tiny splinters. But in settings where this habit is considered impolite—especially in Japanese dining etiquette—it can read as a judgment on the restaurant: you expect its chopsticks to be so rough or cheaply made that they need extra work before they are usable.
The implication comes from the sequence of actions. The restaurant provides the utensils; rubbing them signals that you do not trust their finish. Even if you mean only to make them smoother, the gesture can look like a complaint made before you have tried them.
Check first, then respond
Disposable wooden chopsticks are not always perfectly smooth, so the concern is not imaginary. But rubbing them automatically can create friction and scatter wood dust without fixing a genuinely jagged edge. If the chopsticks feel comfortable, simply use them. If a splinter is obvious, set them aside and ask for another pair rather than making a display of sanding them down.
Etiquette varies by restaurant and region, and a single gesture will not always be taken as an insult. Still, the small pause before rubbing is useful: it distinguishes a real problem with the utensil from an assumption that the restaurant has served you something inferior.
