A/N Maybe it was just me but I felt as though Sam's hair got a little shorter in season 10 (freaky, I know). Here's a silly explanation for that.
Hair Today, Gone Tomorrow
"Hey Sam, do you want breakfast, or-"
"Dean!" Sam jumped and spun around, his expression oddly guilty as he flung the pocket mirror he had been holding onto his bed. "You mind knocking once in a while?!"
Dean raised a suspicious eyebrow. "What, I interrupt you putting on your makeup or something Samantha?" He smirked. Then he noticed something that made his jaw drop open in utter disbelief. "Hold on a second... dude, did you get a haircut?"
Sam's hair had been growing for about as long as Dean could remember. He had always opted for a shorter style himself, it being (as John had told him) more practical when hunting. Hair too long was at risk of breaking FBI regulations, although Sam's hunting, to Dean's continued chagrin, had never suffered much for his regulation breaking hair do (something which he pinned on the puppy dog look he liked to employ so much when interviewing witnesses).
Now though Sam's hair was definitely shorter. Still pretty long for a guy (so at least Dean hadn't lost teasing rights), but at least a good inch less than it had been yesterday. Weirder still was the fact that Sam himself seemed to be just as confused as Dean was.
"Yeah, I er- I guess I must've visited a barber or something." He shrugged, seemingly uncaring, but Dean didn't miss the undertone of unease to his voice. "So, er, what's for breakfast?"
"No way Sam. You don't remember?" Dean asked, grinning at the thought that Sam, of all people, would find it so easy to forget a recent hair appointment and refusing to let the subject change. "What you just woke up today and it was shor-?"
He broke off, eyes widening in realisation.
Aw crap.
"Dean?" Sam asked nervously, as his brother's expression grew suddenly angry. "You okay man?"
"We need to talk," Dean growled. "Now."
Sam glanced around because, though his brother was looking him straight in the eye, it felt as though the question wasn't directed at him.
"Er... we are talking."
"No." Dean shook his head. "We need to talk."
Sam's eyes flared briefly with an electric blue, then focussed on Dean with the steadfast intensity he had now come to associate with the angel currently taking up residence in Sam's body.
"Dean," Ezekiel greeted him. Then he took in the clenched jaw and furious eyes. "Is there a problem?"
"Yeah, actually, there is." Dean jabbed a finger at Ezekiel's - Sam's - chest, and yelled, "What the hell are you doing giving my little brother a haircut Zeke?!"