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.
Anvilicious: Everything we see Brandon do has something to with his sex addiction. It also implies that porn is a dirty, dirty, shameful thing that even his horndog boss finds objectionable. In a film that for the most part steers utterly away from any "if X then Y" reasoning, "Porn is for sex addicts" stands out as an odd apparent stance.
It is worth noting that Brandon becomes significantly more self-destructive once he removes porn, which had previously functioned as a release valve.
His boss also seems to be reacting more to the actual genres of pornography on Brandon's hard drive, finding the fetishistic nature of it to be confronting. Still an unusual emphasis given the rest of the film's subtlety, but it may be more to highlight David's hypocrisy than it is the film's message.
David also makes a point of explaining that it is having (and using) porn at work that is the problem. Considering the porn was likely what gave the company system a virus in the first place in addition to the innappropriateness of masturbating in a workplace, he isn't exactly out of line.
David's porn addiction is presented as more of a symptom of his sex addiction, as opposed to a cause. The "If X then Y" reasoning makes sense here - sex addicts would obviously watch a lot of porn, and in some cases go way overboard. So the problem is not porn, but the fact that David goes way overboard with it. Whether it's sex or porn, a certain amount in moderation is ok, it's only bad when you have too much or are obsessed with it.
Award Snub: Michael Fassbender and Carey Mulligan both went unlauded at the Oscars. The film's NC-17 rating probably had something to do with this.
Fetish Retardant: You want nudity, it's there by the truckload, but the sex is presented as an alien, desperate thing, and the nudity in non-sex scenes has far too much Incest Subtext to ignore.
Incest Subtext: Brandon and Sissy's relationship is waaaaaaay open to interpretation.
For example: Brandon takes Sissy's scarf and sniffs it after he discovers her in his apartment, they show little disgust at him seeing her naked, he straddles her in nothing but a towel after she catches him masturbating (The scene is very reminiscent of attempted rape, including Sissy's panicked reaction). He lovingly (and not in a brotherly way) watches her perform at a club. He also reacts to her having a sexual relationship with his boss as if he's jealous. Sissy also notes his odd behavior towards her in dialogue:
Sissy: It's like I'm always making you angry, and I don't know why.
The film gives almost no backstory on the characters, leaving it to the audience's imagination to fill it in. The question if actual incest happened, or Abusive Parents are to blame for how screwed up the siblings are, has caused flame wars in even more distinguished film forums.
Especially the scene near the end where Brandon abandons Sissy for a night with prostitutes and we only hear the haunting music and Sissy's voicemails to Brandon.
Enhanced by a separate tearjerker moment where Brandon rushes home expecting to find a suicide note by Sissy that she jumped under the train, but instead finds her bleeding out from self-inflicted wounds in the bathroom.
Unfortunate Implications: Some people took issue with the scene where Brandon goes on a "bender" and has sex with a man, due to the apparent suggestion that gay sex is rock bottom.
It's not the fact that it's gay, though - it's rock bottom for Brandon because he's having sex with people he's not even attracted to just to get some kind of release. (Compare to how drug addicts might use any other drug to get high if their drug of choice isn't available.) Replace gay sex with any other sexual activity and it still works.
It would still work if Brandon was gay, and replaced it with heterosexual sex.
This is a strange case considering the director doesn't seem to have any issue with homosexuality (see his short film Bear.)