At least there's a piece of cloth covering the crotch just in case any leakage happens.
I heard women replace their underwears on a monthly basis. Sometimes the yellow stains or period stains can't be removed or the elastic band just deteriorated. It's cheaper buying a whole new pack than bleaching the shit out of it. Otherwise there's the disposable options as well. I'd be lucky finding a pair of used underwear left behind at a bar.
If a guy tells a girl he doesn't have underwear on she might freak out. It's like saying your trousers are smeared with smudges of poo, drops of pee and possibly leftover precum. Underwear for both sexes is basically a hygiene layer that protects your favourite pair of pants or skirt from your excrements. Not to forget it absorbs all the sweat from your balls.