Dean: He would go for babe or sweetheart. He may be stubborn, but he really does know how to make you swoon. You called him handsome, or babe as well. He didn't mind it one bit.
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Sam: He would probably go for something like sweetheart or honey. He, like Dean, knows how to treat a lady. You would call him moose because of Crowley, or Sammy. He was the only other one he would let call him that.
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Castiel: He didn't get nicknames at all, so he'd call you by (Y/N). If he was feeling lucky, he'd call you darling. You'd call him angel or wings. That was just who he was to you.
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Adam: He was a sweet guy, so he'd go for honey or baby doll. You loved it, and it always made you blush especially if he said it awkwardly. If he was being awkward, you'd call him sweetie or honey as well. It was only just.
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Charlie: She'd call you something like darlin' or princess, or Ron. You were the Ron to her Harry Potter, which is why you got it. You would call her Potter, braveheart, or nerd. It was all interest based.
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I hope you like this one