Here are some.
Be Careful What You Wish For by spike_spetslayer
http://dark-solace.org/elysian/viewstory.php?sid=1172&ageconsent=ok&warning=5Buffy's birthdays never turn out well and Dawn's made a wish that everyone would tell the truth for once. Episode spoilers for "Older and Far Away" (Season 6). Answer to Bloodshedverse challenge #140.
These sort of fit since they are funny and have to do with the episode.
What Richie Said by Aisalynn
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=34298Summary: Buffy reluctantly visits Richard in the hospital after her disastrous birthday party, and hears some astonishing information. ---Written for Seasonal_Spuffy, set post Older and Far Away.
This second one is one of the most hilarious stories I've ever read.
Gordian Knot by Slaymesoftly
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=32876Summary: What if Buffy had wanted to talk about Halfrek after the interminable birthday party?
Never Have I Ever by Coquine
http://www.bloodshedverse.com/stories.php?go=chapters&no=6591One-shot. Extremely thin plot. Borderline sillyfic. Set during Older And Farther Away and the never-ending birthday party, the Scoobies decide to play a round of "Never have I ever…" and wackiness ensues.
I haven't read this one. It's complete and was in the humor category.
A Rocking Birthday » by ness345
http://www.fanfiction.net/s/2641640/1/A-Rocking-BirthdaySet during 'Older and Further Away'. Not only are they locked in a house with a monster after them, but the Scoobies find themselves bursting into song, again. SPUFFY