As for me, it’s the fog on the lens. Cold weather, warm weather, wearing a scarf, sipping a hot drink, and cooking are just five of the many, many ways you can fog up your glasses.
I think the most challenging part is for the makeup. It will be very hard to put on the makeup with wearing my glasses. Worse still, I cannot see clear if I don’t put on the glasses first, which could ruin the makeup to some degree.