Ehh … It’s more likely etiquette to not descend on the rolls like a starving Labrador retriever. Much of manners is about self restraint and making oneself ‘small’. The idea is that you wait a minute or two, so it’s not like being at the Chinese food buffet when a fresh load of sweet and sour pork comes out. Everyone piling in for the rolls is undignified. It’s related to the idea that even if you really want that last roll, you ask if anyone else would like it before snatching it for yourself.

… but judging someone for grabbing one when they come out? Pretty prissy.