I can say that depending on the mood of the woman that crossing the line is kind of hard to do if you already know ahead of time that she is attracted to you. There are defiantly more hardcore things to say than others but it's really just a feeling out thing that you will learn from doing it. Woman are very forgiving people, thank god, and will work with you for the most part
. Like someone said above the most important thing is have fun with it and all will be well. Start off with soft porn talk then move on the XXX.
Starters:
Damn you look sexy in that!
Your body is so incredible I would love to see more.
etc.
Some nice things that always works for me that are more "dirty" would be, coming up from behind the woman, in public, and putting your hands on her hips and whispering in her ear things like,
"Your body is so hot my cock is throbbing thinking about all the things it could do for you."
kiss her softly on the neck and say,
"I would so love to taste every inch of your body."
Or "I would love to take you right here and now."
I have found that, for the most part woman like a confidant man and one that feels in control and also when you talk dirty it's not always the best thing to tell them exactly what you want to do but leave it a little vague so that there imaginations can do some of the work and therefor makes them more involved in the fantasy.