Thinking of teenchesters, well John noticing the difference between Sam and Dean.
Sam's 14 and has hardly looked at another girl, Dean at this age was always chasing after them(and still is quite the ladies man) and John had to remind him repeatedly the importance of condoms and safe sex. He wasn't ready to be a grandfather and he knows Dean was most definitely not ready to be a father at 14 or now.
Sam's quiet, bookish, only talks to Dean or when he's snarking back at John.
Dean on the other hand has always been brash and very confident of himself, actually reminded him of Mary.
She was the one who had asked him out after all. Sam's too much like him. Even if he don't want to hear it.
They're in a new nowhere town, some diner, Sam's face lit up when he saw the jukebox and John gives him and Dean some quarters to play whatever.
It's a pleasant evening, they're all talking and joking, the boys are being boys, they almost feel like a normal family.
Sam gets up to pick a song and John notices a boy maybe around Dean's age talking to Sam and he recognizes the body language.
Sam's blushing and trying to talk but John can tell he's stuttering and then it hits him.
It doesn't bother him, so Sam's different than Dean.
But now Dean turns around and his shoulders tense and he's getting up, acting more like a jealous boyfriend than a brother.
He's standing in between the two and Sam is visible upset and embarrassed. He practically stomps back to their booth.
Dean saunters back, a smirk on his face.
Sam doesn't talk the remainder of dinner.
Dean ends up sneaking off with the waitress.
And John has no idea what the hell he just witnessed and what's going on with his kids.