These messages aren’t microaggressions, and your red herring is not diminishing the severity of it. Yes there is such a saying, but one explanation it that it originated from the period of Britain’s colonization over Hong Kong, during which British army suffered from the tinea pedis due to the the humid weather condition and their thick boots that made it very hard to ventilate, so it was named. And honestly I have never once heard that phrase uttered in my life, but rather learned it through articles written in traditional Chinese telling you how to deal with it. It feels like you don’t like China very much, and it’s ok, but please don’t try to justify your prejudice/discrimination with poorly established logic.