Viridian, characters in your stories engage in sexual insults and assault. That's realistic. Sexual insults makes people feel awkward and embarrassed, so it's sometimes left out of fiction that has an audience old enough for it, but because it's awkward and embarrassing, it's valuable fodder for cheap shots. I'm not going to argue that nobody gets raped in a race war because that would be even stupider than most YouTube comments. But it does seem too frequent or too intense sometimes. The Halloween incident is a good example of this.
Resorting to verbal sexual harassment, especially the kind that has no basis in reality*, is ridiculously crude and juvenile, so it fits Malfoy in a lot of ways. Still, I think it's out of character for him to be so graphic and detailed about a topic he's never heard commenting on in canon. We won't ever know for sure, because Rowling couldn't write him that way if she wanted to, but just because absence of evidence is not evidence of absence doesn't mean the opposite is true. I mean, in book two, he actually thought "you've got a girlfriend!" was a real insult.
I know you had to step up the insults because Hermione felt secure in her friendships with the boys, but jumping from "ha ha, you have no friends!" to "you're having sex with all the boys you know" is an astronomical leap. Also, Hermione went and cried in the bathroom in the original book because she actually didn't have any friends. Since she does in this version and knows that Malfoy is completely making things up, it seems like she would be angry and embarrassed--would that really provoke the exact same behavior as eleven years of misery and loneliness boiling over?
I realize that you were also probably motivated by adding more realism. Like I said above, racism and sexual violence have close ties. Rowling's racism metaphors were clumsy and she probably had barely considered them when writing the first book. Trying to incorporate them more smoothly and integrated throughout the whole story is laudable. But for the reasons I listed above, I don't think that was the way to do it.
It feels like you upped the ante to make Harry's victory more dramatic and make him look better by making Malfoy cross a line. Making your hero heroic and your villains villainous is not bad storytelling, but the way you did it seemed gratuitous and out of character for Malfoy.
This community seems pretty tight, this is obviously a very serious and emotionally charged topic, and making a whole new account and topic for it on his personal forum feels uncomfortably like a melodramatic public calling out, so I understand if people feel like I'm attacking Viridian, but that is absolutely not my intention. I'm questioning an aspect of his writing style, not his character. I brought this up here because I know this is a good place for discussion. If I thought this fit in another thread, I would have posted there. I actually enjoy almost all of Team 8 and NoFP, which is why I'd really like to hear Viridian's thought process for that scene.
*This isn't approval of slut shaming. It just takes slightly more subtlety to at least know your victim's sexual history or personal desires than to use "you're a whore" as a goto, even though both are totally despicable.