red flag

What it means

A "red flag" is a warning sign in someone's behavior or personality that suggests potential trouble, especially in dating or friendships. Pointing one out means flagging a trait others should be cautious about. Comes from naval signal flags meaning danger.

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Examples

• He's still texting his ex daily, that's a red flag.
• She was rude to the waiter, immediate red flag for me.
• No friends and blames everyone else? Red flag city.
• Bro listed seven red flags and called them preferences.

Where it comes from

A long-standing English idiom from racing and military signaling, but it surged as relationship slang on social media in the late 2010s and became a Gen-Z dating staple.

Related slang