Doppelgangland.
The title is taken from the 31 Days theme for October 10, 2008. Spoilers for the Naoto arc of the game.
Tatsumi Kanji has come to realize that one of the reasons why he gets so upset at Hanamura Yosuke's not-too-subtle jabs at his sexuality is because it's entirely possible that his upperclassman is being a big, fat hypocrite. It was impossible to protest back in the day, before he realized that Shirogane Naoto, his Number One Extreme Crush, had boobs and was actually very much a girl – it would have been rather close to a pot calling a kettle black, as he has heard Yukiko pointedly remark whenever Chie goes off on a spiel about how Yosuke can be such a freak when it comes to martial arts movies. Now that he was sure he was straight as an arrow all the way, however, and apparently so straight that he can sense a girl even when she's trying to NOT be a girl, Kanji feels a whole lot more comfortable with lashing back out at Yosuke whenever he starts ratting on Kanji's less manly habits (read: sewing), because seriously.
Seriously.
The way Yosuke calls Seta Souji "Leader" and the way he talks about the other boy's manifold talents especially when it comes to what he can do with his hands, the only words that come to mind are gay, and gay, and definitely Gay.