Random porn question

Why do the actors and actresses always refer to their body parts using the third person? For instance, if my neck was sore and I wanted some girl to rub it for a few seconds, and she agreed, I wouldn't scream at her, "Oh, yeah, rub that back!" It's my back, so I would use "my." And yet, in porn movies, it's like they're disassociated from their own body parts.