Your Sister's Sister (2011)

Your Sister's Sister (2011) follows a man whose life is terribly sad after the death of his brother. His friend sends him on vacation to her dad's cabin where his friend's sister incidentally winds up staying as well. The two of them are there together and hit it off over their revealing weekend. Mark Duplass plays a sad man very well - and a naked one! He gets shirtless in a small bed to have sex with his friend's sister. Kinky!