you didn't specify what pairing, if any, you r looking for, but here are a few humorous fics:

Destiel by entangled_now (http://libraryofsol.livejournal.com/174563.html)
Summery: In which Sam is an Uncle and everyone has gone mad Dean/Cas

Sam is Genius (Everyone is Dumb) by peroxidepest17 (http://www.fanfiction.net/s/6659715/1/Sam-is-Genius-Everyone-is-Dumb)
Summery: Dean is doing stuff. Castiel is getting stuff done to him. It seems like the only one who understands what "stuff" actually means is Sam. Sometimes it's hard being the smart one. Dean/Cas

Come on, baby, let me know by scribblinlenore (http://scribblinlenore.livejournal.com/375601.html)
Summery: They don't just have to pretend to be gay. They have to be the gayest! Sam/Dean

Thanks for pointing out that I didn't say what pairing, I'll fix it now. Also, thanks so much for the recs!

(None of these fics are Wincest)

#4:
You Would Cry Too, If It Happened to You (http://superbadgirl.livejournal.com/525103.html) by superbadgirl
The Maiden Voyage of the S. S. Bad Touch (http://sunspot.dreamwidth.org/19440.html) by sunspot
High-Minded (http://alethialia.livejournal.com/222768.html) by Alethia
King Winchester by William Shakespeare (http://azalaea.livejournal.com/2448.html) by azalea
Adventures in Diplomacy (Or How Castiel and Crowley Got Stuck On Earth Helping With the Cleanup) (http://www.fanfiction.net/s/5987728/1/Adventures_in_Diplomacy) by Pero
Vena Amoris and Other Old-Fashioned Bullshit (http://pyrebi.dreamwidth.org/35205.html) by pyrebi

1 and 6 in some cases
Sam is so sick from the trials, Dean is afraid he's going to lose him. All Dean wants to do is take care of his little brother. Sam finally realizes how much Dean needs this and lets him. Suddenly they are too close, too lonely, too connected, and things happen.
http://m.fanfiction.net/s/9282641/1/Sam-s-Breath
In the bunker, while Sam is slowing fading from the trials, Dean claims the untouched part of Sam for himself.
http://melungeoned.livejournal.com/50157.html
What's Christmas without a curse?
http://wincest.livejournal.com/3957061.html
Prompt: Sam's hurt both hands, so Dean has to shave him. Having Dean that close to him, focused with that little concentrating frown, breath warm on his face, Dean's competent hands tilting his head and angling him exactly the way he wants him -- well, Sam's not doing too well right now pretending he's not attracted to his brother. And he's only wearing boxers, Dean's bound to notice. Dean's going to have him all figured out. Dean is amused and turned on and there is a slow, sensuous first time with bottom!Sam. No teen!Sam, please, canon timeline.
http://strive2bhappy.livejournal.com/5224.html
Dean is hexed to silence. While Sam is trying to figure out the why, how, and how to fix, Dean is forced to communicate with him on a different level. Dean stepped on a witch's flowers. Turns to wincest.
http://candle-beck.livejournal.com/116032.html
This one is funny
http://tebtosca.livejournal.com/21393.html#cutid1
This one is funny and sad and sweet
http://archiveofourown.org/works/721859?view_adult=true
Dean is actually courting Sam, who is clueless. But he catches up. Shower sex, first time wincest.
http://archiveofourown.org/works/721761

2.
Sam is jealous and finally lets it slip that Dean takes off with whores every couple of weeks instead of getting laid everyday. Manhandling
http://archiveofourown.org/works/722063/chapters/1339383
The last time he checked, 'Hey, I'm having weird dreams about plants and I kind of want to run into the forest and fuck until my dick falls off, whaddaya say?' is not the best way to get his brother to take him seriously. Sam POV.t.
http://veronamay.livejournal.com/647530.html
Blow Me Verse Series of fics in which Dean and Sam have sex with each other, even though they totally aren't gay. According to them, anyway. Adult
http://rockstarpeach.livejournal.com/80400.html
A bad hunt, a close call. Sam is furious with Dean and forces a confrontation. Dean punches, then kisses.
http://smash86.livejournal.com/3530.html
Kind of a mix between 2 and 1- this one is really out there, but I think it works.
He’s the only one who gets to call him that, and when he stops, Sam feel like he’s withering inside. Lucifer has risen and Ruby has run away, but rogue angels and a legion of demons are still the least of his worries. He just wants his brother back; because there is nothing in the world like being Dean’s “Sammy”.
http://ladycrystal-c.livejournal.com/26118.html
Rough first time. Both accuse the other of being sick fucks while they are beating/biting/fucking each other into submission.
http://blindfold-spn.livejournal.com/2172.html?thread=2869884#t2869884

4
Boys are roofied
http://archiveofourown.org/works/181717?view_adult=true
Sam suppressed a chuckle, and decided not to point out that no matter what was going on now, or would go on at any point in the future, Dean was still the one that took it up the ass first, because that wouldn't get him anywhere. Besides maybe a trip to the Emergency Room
http://www.fanfiction.net/s/5255438/1/You_Know_You_Wanna
Boys lose their voices- this is notes and pics they draw to communicate. I LMAO everytime I read this.
http://masterlist415.livejournal.com/72293.html
This is one of the funniest ones I've ever read.
Boys are hit with sex pollen and, not knowing what else to do with them, Cas takes them to Bobby's- Bobby POV
http://electricalgwen.livejournal.com/94820.html?view=1289572#t1289572