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.
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!
For many, the issue wasn't that Portman won the award, but that publicists tried to cover up the fact that part (it's debated how much exactly) of the dancing in the film was done by a dance double. Sarah Lane (the double in question) states in this interview that Portman deserved the Oscar for her acting performance, but feels that it's degrading to the ballet industry to insinuate someone can master dancing skills like hers in just a year and a half. After Lane did a small interview for Glamour magazine, one of the film's producers rang her up to tell her to keep quiet about her role in the film until after the Oscars.
Hell Is That Noise: Those whispers that always seem to be around Nina and the sound of Nina's nails being cut, but especially THAT DAMNED LAUGHTER.
The exaggeration of Nina's breathing that seems to show up every time she is under pressure, which is the majority of the film.
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.
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!"