“That's... that's great, Sam” is all Dean manages to get out before John cuts him off again, reaching out to physically turn Sam back to face him when he shifts away towards Dean because this isn't over, not by a long shot.
“Don't change the subject, and don't try and be cute either. You had orders, boy.”
“Dad, maybe...” Dean tries again, though why he's bothering he doesn't really know – probably because Sam at least tried to apologise, if that's what that was (Dean really hopes that's what it was, that he's not migrated from keeping the peace to being used as a token in whatever game the other Winchesters are playing, to having them tug at his loyalty and try to score points by making him betray the other to their face. Because that's not going to happen, not if he can help it, but this is one of those 'rock and a hard place' situations)? - and again John cuts him off without looking away from Sam.
“No, Dean. I've had it Up. To. Here with your brother's attitude. He was supposed to stay put and keep researching."