Dean and John misunderstanding
I'm looking for a story where John leaves the boys with another hunter while he's on a hunt. Dean calls John and tries to tell him that the hunter wants Dean to do sexual stuff with him in exchange for having them there, but John misunderstands and thinks Dean is trying to get out of research or something. Dean does what John says but when the other hunter wants Sam to join in too, Dean immediately leaves. Later, John finds out and is horrified that Dean thinks he would ask him to do that and he goes and gets revenge.