Humay,
I'm not sure if "appropriate" is the right word, but it can be "acceptable." Whenever I chat with a girl, I always try to gauge her style first though. Don't drop expletives right off the bat, but if she happens to drop one herself (or you overhear her and her friends dropping them), then dropping one or two in your conversation at "appropriate" times can help set the vibe that you are laid back and not picky about your conversation.
Of course, if the girl is heavily religious or extremely conservative, it's more unlikely that she'll use an expletives. In these cases, I would avoid using any if at all possible.
Also, if you choose to use them, make absolutely sure you are comfortable using them. If you are using swear words uncomfortably, people tend to notice, and it becomes more awkward than anything. So make sure you are comfortable with the way you like to talk.
Cheers,
Franco