The traditional meaning when a woman said "no" to a man was (arguably) that he should try harder, be more persuasive, that she meant "maybe".
A man's defence might be "Yes, she said 'no', but she was just 'playing hard to get'".
The response to this attitude was a political campaign by women to tell men that "no" actually means "no". It is a sign of non-consent.
As a political campaign, it worked to some extent. But all users of language know that pragmatically, some words can mean several things depending on the context, and that 'no' in fact does not always mean 'no'.
From your example, it seems now that to say "No" is insufficient. You need to specify that it's a "no means no" type of 'no'.