What Does ‘Red flag’ Mean?
A red flag is a warning sign that someone or something may be a problem, especially in a friendship or relationship.
Dating & friendships noun
Examples of ‘Red flag’ in a sentence
- “He never lets her talk to friends. That is a red flag.”
- “A shop with no reviews is a red flag.”
Where does ‘Red flag’ come from?
The phrase is older than social media (a red flag signals danger). Its use for relationship warning signs spread widely online.
How to use it, and when not to
Use it for warning signs, including online scams. It is not a joke if someone is being treated badly.
For parents and teachers
Fine around parents and teachers. Safe, and a useful idea for teens to know. Real worries should go to a trusted adult.
Related slang
Frequently asked questions
What does Red flag mean?
A red flag is a warning sign that someone or something may be a problem, especially in a friendship or relationship.
Where does Red flag come from?
The phrase is older than social media (a red flag signals danger). Its use for relationship warning signs spread widely online.
Is Red flag OK to say around parents or teachers?
Fine around parents and teachers. Safe, and a useful idea for teens to know. Real worries should go to a trusted adult.
How do you use Red flag in a sentence?
He never lets her talk to friends. That is a red flag. A shop with no reviews is a red flag.
More dating & friendships slang
Bestie, Breadcrumbing, Ghosting, Green flag, Pookie, Rizz. Or browse the full A–Z / try the Slang Translator.
Sources
Definition written by VibeDex. Slang changes quickly, so this is a snapshot. Last reviewed 2026-10-23.