Chinese people seem to have a hard time realising that even professional expats and business
Foreigners do not wear a suit and often go with shorts and a T on their day off, does
that make them deechers once or twice per week

On days off you would have to be in a very rural environment to be able to be identified as a teacher in China. Even third tier cities now have foreigner tourists and businessmen. I actually miss the attention that I received a decade ago in China. Even when I am speaking in Chinese, barely anyone bothers to look up.

If you are 'on-campus', it is unusual to see Chinese teachers wearing shorts, even in southern cities. School administrators certainly do have a preference for having their 'teachers' dress up, especially for events of any sort. It's annoying.