These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: Okay, there is a lot of bizarre happenings in this film, but the one scene that qualifies for this trope is Beth stabbing herself in the face at the hospital, simply because the character disappears from the film after that point and the events never brought up again. Most of Nina's experiences can be sorted relatively easily into "reality" and "delusion", but what really happened at the hospital remains unclear. It's also a case of What Happened to the Mouse? in regards to Beth.
Though Nina does find the nail file in her own hand afterwards...
Crosses the Line Twice: Nina smashes (breaks?) her mom's fingers in a door partly by accident...and then again on purpose the next day!
Double Standard: Both this film and Blue Valentine had sex scenes of similar length and graphicness, but only Valentine was threatened with an NC-17 rating.
Everybody Remembers The Part Where Mila Kunis Eats Out Natalie Portman: Or at least, Mila Kunis makes out with Natalie Portman and goes down on her body double. As Natalie Portman put it: "Everyone was so worried about who was going to want to see this movie. I remember them being like, ‘How do you get guys to a ballet movie? How do you get girls to a thriller?’ And the answer is a lesbian scene. Everyone wants to see that."
Fetish Retardant: Remember that lesbian scene in the trailer? Some people may find it horrifying.
Thomas Leroy: We're going to do Swan Lake. Done to death, I know, but not like this. We strip it down, make it visceral and real.
Fridge Logic: Presuming that Nina actually stabbed herself, how did she manage to dance with a piece of glass stuck inside her?
Hilarious in Hindsight: Thomas watching Nina's dance rehearsal and noting her lack of seductiveness, asks her dance partner "Would you fuck that girl?" He just laughs, indicating no. The dance partner is played by Natalie Portman's choreographer Benjamin Millepied, with whom she began a Romance on the Set. They are now married and have a child together.
Portman addressed this in her Golden Globe acceptance speech: "He's the best actor! It's not true! He totally wants to sleep with me!"
Les Yay: What most people are talking about in regards to the movie, sadly. Played straight or subverted, depending on if you think that Lily really is coming on to Nina or if Nina is just projecting her repressed urges onto the more adventurous woman.