Sea sharpening

The act of having sex with a flaccid penis and it only getting hard when it's in the vagina, surrounded by vaginal fluid.

Person 1: "Oh man, I had a few too many drinks last night before taking that girl home."

Person 2: "I take it sex was out of the question then."

Person 1: "Normally, it would be. But she really wanted to do it so I just went along with it and started sea sharpening."