Dean can drink a whole beer down with his eyes closed and shoot darts at the same time. Obviously he hits the bull’s-eye, otherwise who gives a fuck? Hell, I could shoot darts and drink beer with my eyes closed, but you'd have to be crazy to think I wouldn't injure someone. He may or may not have practiced this skill.
Sam is tri-lingual--latin does not count, and he's clearly not fluent in that anyway--he speaks beautiful Spanish and German. "Quiere usted seducirte? Es eso que quiere decirme?" might have been uttered to Dean at some point. He was watching House reruns one day, and when he figured out that House new a greater staple of languages than him (and complicated ones too) he got just a teensy bit tetchy.
Dean started smoking when he was sixteen but Sam bothered him so much about it that he quit cold-turkey. John couldn't figure out why his eldest son wanted to kill everybody for the duration directly after.
Sam has a checklist of places in the world that he wants to go. He's never crossed a single one off, but he keeps it in his smart phone as a reminder.
Dean secretly loves INXS, and watched every episode of Rock Star but was glad when Marty Casey lost out in the last episode because anybody who writes lyrics like "It'll be you and me, up in the trees, it'll be you and I, up in the sky" deserves a punch to the gut not a band.
Sam was a history major. He stayed as far away from classics as possible, even when Intro to Roman Empire got the best evaluations. He briefly considered sociology and political science, but the geek in him won out. He was starting to write his thesis on the frontier and manifest destiny. Sam was interested in constitutional law and civil rights--the environment also looked interesting.
Dean and Sam share a mutual hatred for Law & Order. Both of them think it's too ridiculously depressing to waste time on, and that it takes itself too seriously. Dean also has a secret paranoia of Crime-Scene-Investigators ever since the show started airing.
Sam loves Dave Matthews Band and the Red Hot Chili Peppers. He laments the fact that he rarely gets to listen to them, because Dean always hijacks his ipod.
Dean kind of likes wearing suits. He feels professional in them. Sam can't really stand them. He always winds up with cuffs rolled up, his tie undone, and his collar open.
Whenever the song "Boys of Summer" came on, no matter where in life he was, Sam always thought of Dean.
Dean reads a lot--mostly out of boredom--because he doesn't have the patience to research unless he has to. Rock biographies make him kind of sad, sci-fi novels barely hold any interest, but he has a long standing love affair with Peter Bowen's mysteries. Also, his first introduction to sex was through Flowers in the Attic, a thought that makes Dean more than a little uncomfortable if he chooses to dwell on it.
Sam is lying lying lying lying lying oh yes still lying about his powers. He has them. His bitchier days are not because Dean got toothpaste all over the sink again, but because tamping them down is guerilla warfare against his own concious mind.
Dean loves the smell of women's deodorant but not the fact that he always gets the strange urge to eat it-especially the Secret line with all the fruit scents.
Sam occasionally has babylust, especially when he sees them and they're just old enough to toddle. Dean is good with kids, but he doesn't have a whole lot of patience with them, he finds the notion of having kids a little unforeseeable. He feels like he'll never be old enough for that.
Dean has a nearly perfect memory. Most people who know him find it somewhat alarming. Bobby has often commented that Dean could be lying about everything he claims to recall and nobody could naysay him because they can't remember jackshit.
Sam is a bigger sports fan than Dean is. He was in the Sixth Man Club in college, religiously watched both basketball and soccer, and is an absolute pro at fantasy football. Dean played football in high school because it was a thing you did, and he was good at it. However he didn't have much love or devotion to it.
Disclaimer: Lack of sleep doesn't make me retarded--IT MAKES ME MORE INTERESTING.