The guys from Polar Star decide to do a party to celebrate the end of the first round of the Autumn Election, and they also invite the Aldini brothers and Ikumi. Obviously the three of them are wondering if they shouldn't be disturbed by Isshiki going around in a Naked Apron (not helped by the fact that the others are very used to this).
And to close the night, Isshiki appears also wearing a speedo.
The next morning, Soma and Megumi's reaction to Isshiki suited-up is priceless.
Chapter 62 opens with images of the 8 Autumn Election participants, with shots taken of each character looking badass during the preliminaries... except for Soma, whose picture is of when he dozed off in the middle of cooking.
Chapter 71: The sudden Jojo's Bizarre Adventure parody.
Takumi hiding in a corner deciding if step on Soma's foot.
Betsubara 1 has a section where Soma, Takumi and others discuss their casual clothes:
Soma wears a Hanten (equivalent of going around in pijamas during daytime) in his free time. Fumiou and Megumi picture him as a middle-age guy needing a cup of sake. Fumio then points out Jouichirou used to do the same while Gin lectured him about keeping a good image as an Elite Ten member.
Takumi shows he is a fashionista himself and gets annoyed when he sees Soma's "lack of fashion sense", emphasizing how much of a Generation Xerox those two are to Gin and Jouichirou.
Takumi and Soma's reaction when they see Isshiki's abbility to quickly switch from his regular clothes to his fundoshi with just walking behind a tree. Megumi, however, is used to this and treats it like an everyday normal quirk from him.