I think it was a few months after the height of SARS that I found myself on a business trip to China. When I went to the office restroom, there was a sign that cautioned against brushing your teeth in the sink. Prior to that, I considered it normal since in our Manila office, pretty much everyone brushes his or her teeth at work. After that, I started feeling embarrassed about being caught brushing my teeth in a public restroom.
Flossing is even harder to justify doing in public.