My wife doesn't wear skirts or dresses very often, but whenever she does, I always tell her to take her knickers off in public.
She doesn't usually do it. But she has once
A couple of times, as we were leaving the house, I'd just reach up under her skirt and pull her knickers down to her ankles. She usually pulls them back up again, but on one occasion she stepped out of them and left the house to go shopping commando.