Here in particular, Naishi is the one the reader is supposed to laugh at, even as Tō no Chūjō seeks to make Genji the butt of the joke. This shows that Genji is, once again, beyond reproach and is exceptional in fundamental ways, while women like Naishi, who ask for what they want and seek to have sex with powerful men, are funny. It's also telling that Tō no Chūjō barely seems to acknowledge Naishi; this suggests that he doesn't see her as worth his time or acknowledgement at all, even though her presence is what makes his "joke" even work.