Older Wincest Fic
So, a LONG time ago, I read a wincest fic. It was very, very popular; to the point I consider it a classic wincest fic. Dean is tired of everyone thinking he and Sam are gay together, so he starts going super "no-homo." Sam notices, asks why his name suddenly became "my brother, Sam." He asks why they get separate motel rooms.
Dean lies and says Sam talks in his sleep. Sam freaks out and starts assuring Dean he knows it's messed up, but he's not going to like, molest him in his sleep. Deans like, "wtf? I was kidding." Sam freaks out and locks himself in his motel room.
Dean does some thinking and ends up realizing he's into it. So he picks the lock and goes and talks to Sam about how now "might be a good time for a gay incestuous relationship." They end up having sex.
Later at a diner, Dean suddenly decides it was Sam's attraction to him that made everyone think they were gay.