Like when you and your girl are in line at the hotel desk waiting to check in and get your room keys and she leans in and whispers in your ear, "Is your cock hard because I really want it in my mouth!"

Or -- one of my favorites -- when you're at a M&G and one of your favorite ladies walks slowly by, looks back over her shoulder and quietly says (with a devilish smile), "My pussy is so wet right now and I can't imagine why????"

That's the best dirty talk.  Of course, if she wants to yell out all sorts of nasty things while I am pounding her doggystyle I probably won't object . . .   ;-