Let us never speak of this again by Trekker
Whiskey Worse by Alex Wort
Wouldn't it be nice if there were more stories in this category?
Tell you what. I'll do my best to provide one if you (yes, I'm looking at you, dear reader; no squirming and pretending I don't know who you are) try to write one too.
Core Four (Buffy, Giles, Willow, Xander)
any rating (but smut is nice)
try for a happy ending (but if you can't, I understand)