I joined a personal training session where the trainer was training myself and one other woman. We three were to be alone in a small private gym. The other woman arrived to exercise wearing not one, but two masks and kept them on the whole time, even when on the treadmill.

The mask-free trainer and myself didn't acknowledge the masks, and just exercised and joked with each other as we sweated.

The woman arrived for the second training session and wore no mask and hasn't worn one since.

Sometimes setting a good example is all you need to do.