2011, Brigid Cherry, "Becky Rosen, Fan Identity, and Interactivity in Supernatural", in TV Goes to Hell: An Unofficial Road Map of Supernatural (eds. Stacey Abbott & David Lavery), ECW Press (2011), →ISBN, page 204:
His overt revulsion is caused by the Wincest fan fiction — the Sam-slash-Dean pairing that also alarms Dean in the epigraph of this paper — and to a Dean-slash-Castiel (or Destiel) kink meme in which Castiel has a crab claw for a hand.
2013, Katherine Larsen & Lynn S. Zubernis, Fangasm: Supernatural Fangirls, University of Iowa Press (2013), →ISBN, page 102:
In later seasons, slash fans split between those who shipped Wincest and those who shipped Dean with the (male) angel Castiel, a pairing known by the portmanteau of Destiel.
I'm always happy to write some sappy Destiel one shot (a one chapter story, often focused solely on fluff, or pure cuddles) when writer's block is making work on Phoenix difficult.
As for the ships, currently the three most popular on AO3 are “Johnlock” (Sherlock Holmes/John Watson from Sherlock), “Destiel” (Dean Winchester/Castiel from Supernatural) and “Sterek” (Stiles/Derek from Teen Wolf).
The second — which got more than 9 million online votes and 25,000 comments — was won by "Destiel," featuring Dean and Castiel of Supernatural.
2015, Alice Oseman, Solitaire, page 198:
Lauren frowns. “Mate! I thought we’d agreed on ‘Mori’! Or ‘Tichael’!” She sighs. “Man, your names just aren’t good enough, like, they don’t work, they don’t work like Klaine or Romione or Destiel or Merthur. . . .”