I think anything above "matronly" is being whorish.
These are an example of my day-to-day skirts.
Although when looking for these images, I was amazed at how slutish a full length denim skirt could be. No mater how long your skirt it, it's a rape magnet if it's cut up to the waist band. Or if it's so tight that you can't bend over (although that may make it more difficult for your rapist to get into).