In the context of the sudden popularity of memes inserting Bernie Sanders in his mask sitting in grouchy isolation into a hundred other situations, someone pointed out that an advantage of wearing a mask is that you don't have to make pleasant faces. Bernie's eyebrows and body language leak out his true feelings here, but the point is a good one. Some people may continue with masks for longer than they need to for non-health-related reasons.
My own reading of Bernie in that moment is "I'm done even shaking my fist at the sky." I've never felt closer to the man.
Update: You can also murmur curses without detection. The downside is you might get used to it and keep doing that once the mask is gone.