My reply would be something along the lines of, “I have intention of being in solidarity with the insane.”

Reasons for masks in Japan are to prevent viral spread of flu and the like. Allergies. I used to wear masks for this purpose. Carried three or more with me each day and changed them often. The only that shocked me turns out to be a reason for many. The woman wearing the mask was running behind and did not have time to pit make up on before leaving home, so she grabbed a mask. Japanese women, as a rule, will not leave home, nor even answer the door without makeup. Others wear them due to various psychological reasons. Now just about everyone wears them outside even while exercising. Many wear them in their own homes as suggested.