"I met you on a street corner in the middle of the night," he reiterates. "There's a lot of mystery in that, Twilight Zone." (Or, the one where Tony thinks he knows everything there is to know about Steve Rogers.). Non-superhero AU.
They should have known, really. (Or, the one where Mary is Moran.)
Dean stops for a while, stops trying to feel alive because there's no point anymore, he won't ever. Sometimes he meets a pretty girl that likes to straddle him and pin him down, and he likes those ones, and they're enough for a bit. But then, then there's Castiel. (Or, the one where Dean has an Itch that never really goes away.)
For John Watson, the game is never over. Post Series 3 Coda based on John Watson the adrenaline junkie.