As soon as Jack Harkness realizes he can communicate with Castiel anywhere, anytime just by saying his name first, that’s going to be a flirtation game changer.
It’s 3am and Castiel is chasing ghosts with the Winchesters, when suddenly he hears a familiar voice say in his head: “Somebody’s thinking about you right now, hot wings, and how cute you are when you’re angry.”