When you kiss him passionately and run your hands through his hair.

When you are interested in the violent and gory things that he finds fascinating.

When you are sparring together while throwing snarky comments back and forward. What also turns him on is when you hear a word that isn't used beyond the Wall for the first time, for example: Theon was talking and said the word 'dick,' You innocently asked "what's dick?" "Cock" theon replied. "Ahh, dick, I like it" you replied. Theon, Robb, Jon, and seemingly everyone in a fifty mile radius roared with laughter while you died inside. (inspired by Tormund in 'Beyond the Wall' for this bit)

At first he gets turned on by the slightest of touches but as your relationship gets more intimate he gets turned on by the feeling of your skin rubbing against his.

When you wrap your legs around his waist and push him onto the bed, kissing him all the while. Then he flips you over so that he is on top and...

Many things you do turn on Oberyn, it would be easier to say what doesn't turn him on. However number one is probably when you are dominant in the bedroom.

When you are engrossed in a book. Usually your hair is messy and you are nibbling your lip. Eventually you look up from the book and smile happily at him. He always smiles back and asks "what's happened?" To which you reply with a jumble of words explaining what just happened in the book as fast as possible. While it is relatively innocent just seeing you being so cute and happy makes him want to make love to you there and then.

When you run your hands through her hair after brushing it.