I hear you but this was not the hill to die on. Two years of commuting to NYC during this “pandemic” and NOW I get a Karen type. I’ll consider this a one-off. If it becomes a trend, I’ll consider a different tactic.
Put it on and immediately pull it under your nose and makes sure Karen sees you do that or let the Karen know the average pore size of a mask in 10,000 nm and the virus is about 100nm. Ask him if he had to shovel sand would he use a tennis racket? And not put on your mask.
I’ve done both.