They noticed the next time they were at the house that Bobby looked at them funny.
Sure enough, that night after dinner, once they each had a couple drinks in them, Bobby stood over the brothers with his hands on his hips.
"Now I ain't gonna say this but one time, and we are never gonna mention it again," the older man began. "I didn't sleep through the part where the the siren appeared to both of ya as a brother. You're grown men, and what you do on your own time is your business, but I don't wanna see any tongue, or anything beyond that."
Dean's mouth gaped open and Sam stuttered and floundered.
"B-b-bobby! It's not ... we're not ... we're brothers!" Sam stammered.
"We would never ... are you serious?" Dean demanded.
"I ain't saying you've ever crossed that line, or that you plan to. I'm just saying that what a siren appears as ain't random." Bobby looked from one Winchester to the other. "And that's all I got to say about that."
He tipped his head and ambled off, up the stairs.
Sam and Dean turned to one another, wide eyed.
"It's just ... it's because we were mad at each other." Sam rationalized as Dean poured another drink. "It doesn't mean anything sexual, it just meant the thing we wanted most was to fix our relationship."
"Yeah," Dean nodded, then tossed his drink back.
"Do we need to talk about this?" Sam asked.
"Oh hell no." Dean shook his head and pushed a glass of whiskey in front of his brother.
"Oh thank God." Sam muttered, downing his own drink.
