[He's certainly trying to get a rise out of her. Though he's hoping for a more sexually charged one, not just embarrassing her. They're supposed to be doing the sex thing, after all, so sexy talk is a good idea right?]

I really, really like it when you tie up your hair. It reminds me of what you've done with your mouth before, and it makes me think about doing it again.

[Given his use of indirect language and the blush on his face now, it's probably safe to say that Watanuki's dirty-talk is going to be flowery like this rather than crude. Whoops.]