Irreversible/YMMV

Unfortunate Implications: The film was accused of being filled with homophobia, as the gay characters featured in the Rectum Club are perverts who hit on Marcus, and one of them tries to rape him. While the almost-rapist is beaten to death, another gay man watches and masturbates. Played by Gaspar Noé himself.
True Art Is Angsty
Squick
Some Anvils Need to Be Dropped: Roaring Rampage of Revenge movies are pretty common, and it's rare to show what that'd actually be like in real life.
Nausea Fuel: This film makes few allowances for those that suffer from motion sickness. The vertiginous camerawork and garish red lighting combined with the intense droning soundtrack caused a few people to vomit at the premiere. Low-frequency sound was also used in order to disorientate the audience.
Moral Event Horizon:
- Marcus' initial fight with the suspected rapist, and then Pierre's extinguisher bludgeoning of his face.
- La Tenia when he rapes and beats Alex.
High Octane Nightmare Fuel
Harsher in Hindsight: Something revealed towards the very end -- namely that Alex was pregnant, makes the events shown at the beginning of the film seem even worse.
Fridge Horror:
- The man the camera zooms in just after the extinguisher beating, who smiles? That is La Tenia.
- Just the realization that this happens in the real world.
- Also, one of the most disturbing things about the rape scene is how methodical Le Tenia is; there is no hurry or uncertainty, he knows exactly what he's doing, as if he's had a lot of practice...
Freud Was Right: See Visual Innuendo
Complete Monster: La Tenia, the pimp and rapist.
Anvilicious: Le temps détruit tout.