Although it's par for the course behavior for Shishijima, it boggles my mind that Igarashi would help Shishijima in his perveted attempt to spy on Chiyo (or any woman) naked, even if Shishijima "promised" that he wouldn't look at Chiyo. Yeah, right. Frankly, I was disappointed that these 19-year olds regressed to juvenile schoolboy behavior.
On the other hand, it was good to see Igarashi man up and make it clear to Ookuma that he knows that Ookuma and Chiyo had some kind of past, but Chiyo is now his girlfriend.