Sam and Dean don't hold hands.
Dean will snatch his hand back and glare if Sam tries to hold his hand. Sometimes he'll flinch back when Sam's hand brushes his, because he thinks Sam might possibly be trying to hold his hand. Whether or not they're in public, Dean won't tolerate it.
Sam doesn't mind, really, he just likes to mess with his brother on occasion. Make him uncomfortable, maybe even blush. Then possibly tease him about blushing.
Dean doesn't actually mind, either, but there's no way he's going to admit to Sam that he thinks that holding hands can be kinda nice sometimes. He likes to overreact about it, see Sam's playful smile. Maybe he'll even blush, so he can watch Sam's eyes dart around his face as if he could soak up all of it. Sometimes Sam teases him, and Dean just flushes in a way that makes Sam's eyes dilate as Dean glares as harshly as he can when faced with such desire.
Sam actually prefers not holding hands. The way Dean grumbles at him is adorable, and when Sam gets him to blush and look away, it's almost too much to bear. When Dean's tongue darts out to wet his lips before he snaps out his warning, Sam smiles. Sometimes Dean will bite his lip when he sees the desire in Sam's eyes, and Sam will melt a little inside. Dean will say something harsh about Sam being much more girly, and Sam will respond by crowding him against a wall and demanding that he elaborate on this theory.
Dean loves it when Sam gets aggressive, so he'll push back- maybe toss out a comment like "your hair for one" just to keep the ball rolling. Sam will shove him back against the wall and move in closer so that they're almost touching, his nose a hair's breadth from Deans. He'll glare into those green orbs and wait for the shorter man to elaborate. Dean just barks out whatever insults come to his mind, pushing against his brother to test his strength. Sam will slam him back against the wall so hard his back would hurt for days, or grab a hand full of his hair and pull his head back harshly. Dean will laugh, cough and snicker, grin up at him, and just be as cocky as he can.
Sam loves fighting for dominance over Dean. He knows it's something he can have whenever he wants it, but he likes the foreplay of winning it. So when Dean's breath quickens, his pupils dilate, and he starts to bring up unrelated things in an attempt to continue insulting Sam's femininity without being outright mean, Sam will grind his growing erection against his brother's. Dean's stream of words will falter, and Sam will tell him that he has nothing to prove. He'll say that Dean can think whatever he wants, but that no girl could give him what he needs. He'll accentuate his point with a roll of his hips, maybe accompanied by a rough tug on short hair.
Dean will demand to know what it is exactly Sam think's he needs. His brother smirks, giving him a look that clearly says he thinks he's won. He'll tell Dean in exacting detail what he wants. He'll drop his voice to a vibrating growl as he tells him how he knows that Dean wants him to pick him up and fuck him against the wall as hard as he can. How he wants Sam to forget the meaning of gentle and try his damndest to put him through the wall, how he wants to be trapped and taken. How much he needs a dick in him, needs to be filled and owned and his name pounded from his /Sam will keep talking, a steady rhythm of grinding against his brother's restless hips until Dean cuts him off with a needy breathless plea- "Sam, just fuck me already."
Sam and Dean don't hold hands.