So, a woman is giving you "the smile" and initiating conversation. She might even be doing annoying stuff like spreading lies about you because she likes you. But you don't want to get with her, so 1) what should the goal be (e.g. to hurtfully reject her, or, to just get her to go away and disappear) and 2) what should you say (or not say) to achieve that goal?

Do you just show as little interest as possible, avoid answering questions, one-word answers, etc?

Do you reject her using the exact language with which women reject men ("wouldn't want to ruin our friendship" / "I see you as a big sister")?

Do you mention that you're currently having relations with multiple women in their late teens / early twenties and don't want anyone else?

Do you leave her on 'read' and just not say anything?

etc etc.