It's a phrase that expresses:
* Refusal: It's a direct way to say "No" or "I don't want that" in a slightly more forceful or dramatic way.
* Disagreement: It can also imply a strong disagreement with something the other person is saying or doing.
* Rejection: It can be used to reject a romantic advance or proposition.
The phrase is often used in a more dramatic or passionate way, even if it's not intended to be taken literally as "my darling".