It's probably entirely sexist of me, but it makes me shudder whenever men in fic are described as giggling.

Drunk, stoned, or startled, they can giggle. Otherwise? NSM.

Childish: Tony DiNozzo. The SG guys, not as much.

My God Mrs. Ackles is fit.

Mr. Ackles is no slouch, either. He looks so adorable when he's not!Dean.

Drunk, stoned, or startled, they can giggle.

Yeah, I'll give you that. Although I might limit it to the first two.

Yeah, I've gotten to the point where all the constant eyerolling in fic is bothering me, as blue collar guys don't often show exasperation that way in my experience, in contrast to sarcastic teens and women with humanities degrees.

Sam's an eyeroller. Dean, not so much. He does more of the raised brow are-you-kidding-me face.

I've also read a lot of "he made a gagging noise" as either brother mocks the other, which always sends me to that scene in The Goonies with Chunk telling his story about the movie theatre. Needless to say, it pulls me right out of the story.

SGA's Sheppard canonically does a fair bit of young-seeming things. There are scenes of him playing with toy cars, debating Bat villains, pushing coworkers off of balconies, etc. His quarters were furnished in minimalist college student: musician poster, guitar, novel. I can see where the 13-year-old in a 40-something body fanon comes from.

Dean, not so much. While he likes his pop culture riffs, he seems to unwind by drinking, watching medical soaps, and getting laid, not setting up an RC car obstacle course with Sam.

Both men have dangerous full-time+ jobs that require adult concentration and judgment. But on the off hours, their attitudes seem pretty different.

Dean does actually claim to be Batman. I don't think calling him a teenager in an adult body is at all far-fetched. He may be post-pubescent (cf: porn consumption, masturbation), but still pretty boyish in his downtime.

Or maybe I'm judging adult male pastimes like prank wars and stuffing your face with food as being boyish.

Although I might limit it to the first two.

Startled!Sam giggling makes me want to giggle. I'm totally pro it. Dean, not as much.

He may be post-pubescent (cf: porn consumption, masturbation), but still pretty boyish in his downtime.

He does like whoopee cushions and daring (and double-daring) Sam to drink gross stuff. I think Dean's got a ten-year-old boy in there who didn't ever really get to play. He would probably be psyched to set up some RC car races.

I think Dean's got a ten-year-old boy in there who didn't ever really get to play

That's exactly how I view it. He's got a continual low-level indulgence going on of something he never got to do at the time.