I don't know...? I mean, I guess if you came to school in a short skirt, revealing top, and heels, you'd be perceived as slutty. I usually don't want to look too overdressed/slutty when wearing a skirt, so I usually wear it with sneakers and a cardigan to make it better for school.
yes there is. it should be at least 2-3 inches above the knee because you can still look sexy to show off some legs but if you can't bend over without showing your va jj then its really short and trashy... its always nice to leav some for the imagination... :)
Sometimes its not possible, like if its a school girls skirt, or its to short and you can see the underwear assuming she not going comando, probably not a good idea to go comando when wearing a skirt as well, gust of wind and the whole world is your gyno...meh and its only ok to where em on one day of the year that's halloween, so save up and slut up on that one day, only comes around once a year...
All I know is that when sitting down, its important to slowly change your crossed legs.