A normal world AU where John isn't homophobic, but he treats every man Dean dates the same way a girl dad would
"Ash? The redneck stoner with a mullet? The guy that lives in Ellen's basement? Absolutely fucking not! He's gonna give you an STD just by bein around him!"
"I think Jo's got the eye for ya, and since I don't want Ellen on my ass, you're gonna have to let her down easy. She's too much woman for a guy like you, abd chances are she'll stab you in your sleep"
"I don't want you talkin to that Crowley kid. I don't like his attitude, and his mama's clearly some kinda witch. That boy is gonna string you along and break your heart, and I ain't about to go to jail for putting a bullet through his head."
"No, you're not going to Lisa's house. That's final. You two either have your little study session in your room with the door open or not at all"
"Don't even think about it- Dean, that Cajun boy is a military brat! He's nothing but trouble and noncommitment! And no son of mine is gonna end up a widow to a man named 'Benny'. Not even a Benjamin"
"You ain't seeing Amara again! That woman is too old for you. I don't care if you're a legal adult! While you're livin under my roof, you ain't seeing anyone older than 2 years your senior and that's being generous."
"Here" John hands Dean a taser. "If that new snot-nosed British brat starts talkin to ya, use it on him"
Dean cringes, "Ketch? Gross dad. He ain't exactly my type."
"Yeah, well, your track record is shit, and I saw him eyeing your mom yesterday. I just want you to give him a warning shot for me"
And one day, during the holidays years later, Dean brings home Castiel
And John does the whole "puffed up chest, cold shoulder, critical eye" thing where he's trying to size Cas up
And Castiel, dorky lil dude in a hand-me-down trenchcoat and a crooked tie, meets John's stare every time. Answers all his leading questions and sarcasm with stoic confidence and defiance. Openly presses himself against Dean's side on every opportunity, staring John down as if to dare him to call them out on it
Cas has heard the horror stories of Dean's dating life growing up