Before the pandemic, some Thais wore masks in crowded places i.e. in the trains, shopping centres etc. Some of my colleagues come into the office with masks because they woke up with a bit of a sniffle that morning. Whether they are being considerate and mindful of not sharing their droplets with others, or they do not want to receive any, or they just want to hide behind a veil, let them be. As far as I can see, mask-wearing was never an issue pre-pandemic and shouldn't be one now. If you want to wear it, go ahead. If not, don't.