Girls wearing shortest shorts.
Those that emphasizes the boundary between the butt cheeks to the legs, as shown in the examples below:
some links to some cuties:
https://fhg.met-art.com/2016-06-16/MIRGEA/ http://www.brdteengal.com/galleries/eternal-desire/caddy-featuring-caddy-a-by-arkisi-317.html
http://promo.spunkyangels.com/donna-jeancutoffsnn/1/ http://tools.madisonlain.com/hosted/hitachi_play/1/