Red Flag
A warning sign that a person or situation is going to end badly.
Origin
The phrase has 18th-century military origins โ a red flag flown over a fortress signaled refusal to surrender โ and a 19th-century industrial one (red flags marked danger zones, then later signaled striking workers). In the 2010s, dating and pop-psych writing pulled it firmly into the relationship register, where it now mostly lives. 'Green flag' followed in the 2020s as the deliberate inverse: an early sign that this one might be okay.
Modern usage
Inescapable in dating talk, advice columns, and TikTok content. 'Walking red flag', 'red flag city', 'green flags only this year'. Light enough to use casually, heavy enough to actually warn.
In the wild
He doesn't tip โ that's a red flag.โ common usage
Tags
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Making someone doubt their own perception or memory in order to control them.