Congratulations! I think everyone here just learned the lesson of not thinking critically about what someone on here tells them to do. No offense to any intelligent and experienced guys with low post counts, but generally speaking, if you see a guy with a post count below 30, he hasn't been around long enough to actually figure out what works and he's just pulling SHIT out of his ass (pun intended). Think seriously about what someone tells you to do, or you can end up messing up friendships, relationships, jobs, etc. I've even talked to guys that have been physically harmed because of saying something stupid that someone suggested; nothing like a broken nose to make you think twice!
The girls that talk about sex all the time, get guys saying crap like that all the time. Most of the reason why they do it, is because they want to flaunt their goods and are basically teasing everyone with a dick by saying, "We love sex, but you can't have any with us!" By saying, "You're just all talk, we should have sex and you can prove you're not!" or some variant of that, such as the one you were advised to use, you play right into their hands and now they get the fun of calling you a creep.
The best way to go about this, is the indirect approach. A girl that's so overtly fucking with everyone's heads, will expect direct, it's just like a stripper, or a porn-star (hell half of those women used to be the girls you are talking about, or still are). You fly in under the radar and then pop up once you're safely behind the lines and you achieve victory. If anyone that knows me, is wondering why I would choose an analogy that makes the whole thing sound like a battle, that's because most likely you're not going after this girl because you have feelings for her, cause she's a dirty dirty girl and you just want to conquer her, so that's why.