The meaningful distinction between a red flag and a quirk is whether the behavior involves honesty, respect, or care for others versus whether it is simply a preference or habit that differs from yours. Someone who is chronically late to everything is displaying a pattern that involves how they value other people's time which is a character question. Someone who organizes their bookshelf alphabetically is exhibiting a quirk that says nothing negative about their character. The confusion happens when we apply the red flag label to things that merely make us uncomfortable rather than things that genuinely indicate a problematic character pattern. Conversely we sometimes rationalize genuine red flags as quirks when we are attracted to someone. https://datewise.org/ provides frameworks for making this distinction more reliably by helping you separate your emotional reaction to a behavior from an objective assessment of what the behavior actually reveals about the person's character and reliability.