It involves a BDSM-like scenario in which Brendon gives Ryan, in the gentlest terms possible, a milk enema. It's quite different from most shock stories in that it wasn't intended as such, it's well-written, and actually has quite a large amount of positive feedback.
It is infamous in the Panic! At the Disco fandom and is quite well-known amongst bandom readers in general. Many other fandoms have plagiarized it and made their own versions of the milk fic, leading to it being a locked entry.
2.) Another term for any particular fandom's shock fic.
Dan Howell (danisnotonfire) has read the milk fic, have you?
"Ryan was kneeling in the bathtub..."