I think it may just be because he feels uncomfortable around Zange seeing as how she's tried to jump him already. Lol.
Everything is there for Tsugumi except for the final piece. As I've been saying since the beginning, if he's not blushing and nose-bleeding while checking her out, nothing's going to happen. Their friendship isn't gonna move to the next level until some physical attraction is thrown into the mix.
Now that Tsugumi's seen him naked, maybe Jin needs some payback in a future episode.
