Her: "Let's just be friends."
You: (Calm and slightly amused) "Who are you trying to convince, me or you?"

It works even better if she has said it more than once, then you can add, "You keep saying that. Who are you trying to convince, me or you?"

I have had a woman literally grab me and start snogging the face off me, saying this. Obviously, she does have to like you though, in which case the LJBF was probably a shit test.

Another one my mate, a non PUA natural, taught me was when a woman rejects your kiss. Try again later. If she says no again, just say, "You've already said no. You're repeating yourself now." I tried it and it worked.