" You know bro , I let you talk me into getting naked and pose for artistic pictures just for your benefit to have a few nudes for your portfolio. But now with me in a doggy style pose and you directly behind me with you focusing directly on my pussy and asshole. This crosses the line from artistic to pornographic you know". Yeah , I know but your having fun still right sis ?

that would be my way of playing on the beach

Right in her ass