Plenty of adults who look put together once showed up somewhere with the price tag still on.

Competence at anything social is learned, usually through a few memorable mistakes. The adult who seems to know exactly how to behave has their own story about the wrong clothes, the wrong fork, the label left on. None of them were born knowing, and most would rather you did not find out how they learned.

Ask somebody older about their most embarrassing version of this. You will get a better story than you expect and a more accurate picture of how people get polished. Then be kind to the next person who arrives not knowing.