Red Flag
PhenomenonA warning sign about someone's behavior or character early in dating.
What it means
Red flag is borrowed from sports/safety usage to mean any early warning signal about a romantic partner: rudeness to service workers, lack of friends, contempt for an ex, financial irresponsibility. The phrase has been so over-used that 'beige flag' (a quirky-but-not-bad signal) and 'green flag' (a positive signal) have emerged as variants.
Related terms
Make the first impression the easy part.
Turn the photo you have into a better photo or a short video. Still you, on a good day.