...a tail. You can feel long thin strands of hair around a smaller base. It seems to be attached right at the end of your tailbone. You're confused at first, but realization slowly comes to you. You were drunk, your friends were drunk, and you made the tragic mistake of passing out before they did. Someone glued a phony horse tail to your rear. Where they got a phony horse tail, why they thought it'd be funny, or what kind of goofy-ass meme (no pun intended) you're going to get turned into are all questions that you're too hung over to adequately conquer. Your first order of business is to take care of the business that brought you in here.
You wrap your hands around the base of the thing and give it a tug, but all that happens is a dull pain as the base obstinately refuses to come away. The first hint that something odd has happened comes when, in addition to feeling your skin tugging with the tail, you also dimly feel a slight tug at the tail itself. You rub your eyes and hunch forward, resting your hands on your knees. At the very least you've managed to pinpoint the oddity and adjust enough to finish up.
Following that you stand up and turn on the shower and step in, getting a better look at the offending addition while the warm water cleanses you. You run your fingers along it's base looking for the edge of it, but you're just not finding it. The tail seems to blend seamlessly with your skin with no hint of glue. Realization slowly starts to peek it's head through the solid fog enshrouding your mind. To confirm your growing suspicions you run your hand along the tail. You can feel your fingers running along the entirety of the tail.
"Da fu...?!" you cry out, trying again to tug the thing away, the slick tail sliding through your fingers. This tail, your tail, isn't fake. A real genuine horse tail is growing from your rear. For a moment you're not sure what to do, you just stand there in the shower. A knock on the door snaps you back to reality.
"How long you gonna be in there?" your roommate calls out. Your eyes widen. You can't let him see you like this. Thinking quickly you wrap a towel around your waist, pick up your discarded underwear and hurry back to your room, prompting your equally hung over roommate, fortunately is so focused on getting into the bathroom, he doesn't notice your situation.
Back in your room, you lock the door and remove your towel so you can again look upon the inexplicable appendage. You experimentally try to lift the tail and find that it responds to your intentions. You gaze into the mirror to get a better look at it when you see a note you seemed to have missed. You pick it up and read the loopy cursive handwriting.
It reads:
Morning, stud. Last night was fun. Much fun. Call me soon. - xoxo, Faye.
You slowly approach the note and pull it off the mirror. Flipping it over you see a cartoon picture of a young man with a horse's tail. A speech balloon points at him that reads "I want a piece of tail." An arrow points to the caricature that reads "you". The very bottom of the page has a phone number along with the words "Very soon, if you know what's good for you." You don't remember meeting any women last night, let alone having fun with them. Then again you don't remember growing a horse tail, so it's clear you blacked out. Still this isn't answering the most important question.