People in the comments talking about why would Ichikawa wear that undershirt with no shoulder coverings (IDK what it would be called). However the translated tweet from the author on page 4 says that there was a mistake in not putting in the tone for the collar of the over-shirt and Ichikawa is actually wearing a long sleeve undershirt.
The drawing of Ichikawa with the shoulder-less undershirt is just the author having fun with the mistake and subsequent comments on Ichikawa's fashion supposed fashion choices.
Yamada knows she's pretty but wants Ichikawa to say it
Ichikawa doesn't know he's pretty but if he finds out, we done bois. My man looks like the bottom from a femdom/futa doujin already
Yamada dropping hints that she'll beat yo' cheatin' ass if dare try and get a side bitch, not realizing that anyone Ichikawa would cheat on her with probably would have forced themselves onto him
Also obviously Yamada would be aware she's a beauty. She's a model
@openeeyes I read that expression as more expectant- she's hoping that Ichikawa will say something that makes her feel better, a test he passes with flying colors. Mostly because of the framing- if she was reacting to what he said in that panel I feel like she'd be to the left of the speech bubble rather than the right.
@Kazeiro Going by the chapter where they finally exchange LINE info Yoshida definitely suspects something is up, at the very least. Would not surprise me if all three of them know what's up, but Yamada definitely doesn't know if any of them know.
EDIT: Thinking more, there's a decent potential for an "Ichikawa overhears the friends talking about how obvious it is that Yamada's into him and gets a new wave of 'I can't be with her because her friends will judge her' insecurity" arc in the near future