Wait, lemme see if I got it right: She ment for him to clean it with a napkin, but seen him go straight for it she went along with it so he won't feel embarrassed?
Is Yamada the most perceptive character ever?
Sekine (Moeko) is also pretty high up there (arguably the most perceptive in the series, I'd say), and quite a smooth manipulator, as she demonstrated in Ch61 in setting Ichikawa on the right path towards Yamada's place, and then bugging out when he ran across Yamada so they can be alone together. She made it pretty clear she considers Ichikawa's feelings for Yamada to be one of the most obvious things in the world, and it's been implied Yamada kinda gushes about her time spent with Ichikawa with her friends, though clearly Kobayashi is so super-dense she doesn't get it. But Moeko and Serina seem like they already know, just like Hara.
Most everyone else seems to be at a similar level of awareness as Adachi, who knows Yamada and Ichikawa spend time with each other, but doesn't yet realize they're into each other (Ichikawa being into Yamada is probably about all anyone is willing to bank on, while most probably think like Adachi does at this point that there's no way Yamada would like him back, at least for the time being, even though she's totally been on that path nearly since the beginning of the story, whether she was aware of those feelings or not, and it's apparent if you pay attention to subtle details).