There's nothing wrong with taking the piss out of a girl. That's not negging, you're just showing her you don't need her validation.

You know something I find blasts my attraction with girls? I tell them to fuck off.

I mean, I don't suddenly come out with it. Its not like:

CO: So yeah, travelling around China was great, wonderful place.
HB: I'd love to do it, it sounds amazing.
CO: It really is, just a fascinating country. By the way, fuck off.
HB: Er... What?

...Not like that. I mean if a girl says something I want to call her out on, I'll readily use the words 'fuck off'. I'll tool her by telling her to fuck off as part of general banter. Not because its a line - I just broadly tell people to fuck off anyway!

As far as I'm concerned it isn't a neg. It just tells the girl I'm not gonna bother being all nice and polite with her, and I'll happily challenge her in no uncertain terms if I think she's talking bollocks. I won't say to her 'I don't quite agree with you' or anything. I'll just say 'Fuck off'.

I wouldn't bother knowingly trying to neg a girl.