Spot it early. Say it clearly. Mean it.
A red flag is not simply something you dislike. It is behaviour that predicts future harm — a pattern of disrespect, control, deceit, or escalation that reliably gets worse rather than better. Distinguishing a genuine red flag from a preference or a bad night is the skill that saves years.
The behaviours that most consistently predict trouble are early: love bombing that outpaces actual knowledge of you, contempt disguised as jokes, rewriting of shared events, financial secrecy, isolation from friends, and a stated history in which every previous partner was crazy.
Boundaries are the enforcement mechanism. A boundary is not a request for someone else to change; it is a statement of what you will do. 'Please stop yelling' is a request. 'If you raise your voice, I will end the conversation and we can pick it up tomorrow' is a boundary — and it works because it depends only on you.