Yamamoto looks confused, but then, he doesn't know who Bo is, but he's assuming she's promiscuous by what Kenzi is sharing.

"Haha! Maybe only people like her should have been brought here!" People of age with experience who don't let softly suggestive jokes fly right over their heads. Now, there's something youthful about Kenzi's face, but Yamamoto has a feeling that the woman before him probably has some experience with sex. Sure, she may not be comfortable with Ariel, but he almost feels compelled to ask her for advice on the matter. That might make the illusion that he's relaxed disappear completely, though.