J2 role playing as Sam and Dean. Not necessarily the usual casting. Can be silly mocking of characters, or one of them gets tired of the other always stealing his character's clothes, or arguing how Sam and Dean like sex, and they get into it and into demonstration. I see some heartfelt masturbation side by side, talking about the characters, or perhaps - not just...

OR J2 of Dean and Sam roleplay a kink they read in fic. One of my favorite SPN plots.