Dirty talk during a lap dance

During the last couple sessions with my CF, she's asked that I talk dirty to her while she's grinding on me. I didn't really know how far to push it but the dirtier I got, the harder she was grinding. I've just been inching up the scale of dirtiness, not really sure where the boundary is to offensive to her. But so far we haven't gotten there. In a way, it's kind of cool to have this added dimension to our couch time. The last time she basically clamped her legs around me and shook orgasmically when I said "I want to pump your cunt full of my cum." Who knows if it was real or fake, but it was effective. What's been your experience with dirty talk to dancers and have you ever crossed a line that they didn't like? Part of me is worried that I could mess up this good thing by saying something too dirty.