Do We Have This One?
You know the one -- The Pink Ranger's skirt. She's wearing a skintight bodysuit, she does NOT need a skirt at all for modesty or any other purpose, except as a Tertiary Sexual Characteristic
Does not apply to really short skirts that still provide coverage over bare skin (no matter how little), or skirts that are embellished enough to count as a fashion statement -- Sailor Moon's skirt doesn't count, but a miniskirt worn over pants does.
Also does not apply to 'skirts' that are really just an untucked shirt, ala Hey Arnold!