The premise of the scenario feels kinda forced. It's like, rather than just put up unambiguous signs, it's some shitty signs that kinda look similar, AND the shower rooms for each gender were switched, AND they rely on some coach explaining it exactly when Nagatoro isn't present, AND the friend has the magic ability to smell boys, AND she also has the magic ability to distinguish lingering boys' scent from an actual boy being physically present in the room, AND they completely disregard the possibility that the boy walked in by mistake even though they were just discussing how stupid and confusing the signs are and are hellbent on having them expelled if they are found, just so the stakes are as high as possible. It's all just so insanely farfetched.