Surprisingly enough, they don't immediately leap for each other's jugular, so we must endure an extremely chatty round of accusations and counter-accusations before they actually start kicking the crap out of each other. Dean goes first, for whatever reason, and long story short, the Sam he knew is gone, replaced by the remarkably broad-shouldered corpse-fucking LIAR he now sees before him. Sam's retort? Basically, that Dean came back from Hell a whiny little piece of shit who's worthless as a hunter, because he's spending all of his time in the bottom of a bottle feeling sorry for himself and all of those souls he tortured over the past forty years. "Boo. Hoo!" Sam snots, and then? It. Is. ON! "VIOLENCE!" Dean whips the hunting knife at Sam's head, and how he missed a target that large, I'll never know, but Sam manages to duck it in order to kick Dean's ass. Yep, for once in his miserable life, Adult Sam fails to suh-huuuuuuck at the hand-to-hand, and the results are glorious indeed as he slugs and punches and whacks and thwaps and bomps and stomps and slams Dean's stumpy little ass from one end of the room to the other, until they end up where they started at the front door. "UNREPENTANT ACTS OF WANTON VIOLENCE!" Unfortunately for Sam, Dean manages to flip him around so his back's against the door, and then Dean -- with the last of his strength -- charges, hitting Sam so hard that the door blasts off its hinges, and they both end up on the floor outside, Sam far more winded by the experience than Dean.