So...it would be unrealistic for Marigold and Hannelore not to sleep together...because...Hannelore is creeped out by semen (stipulated)...Angus is a prick (stipulated)...Marigold, Unwashed Fujoshi, has a fairly good chance of being bi (stipulated...although "extremely" is pushing it, hard)...and they're watching vaguely ecchi anime together (obviously stipulated).
So let's break down your way of thinking.
1. ASSERTION: Marigold is bisexual.
2. ASSERTION: Hannelore is unlikely to have sex with a man in the near future.
3. ASSERTION: Angus is an asshole.
4. ASSERTION: Hannelore and Marigold are watching pretty boys have highly stylized sex.
5. INFERENCE: ???
(All right, I'll be charitable here.)
5. INFERENCE: From 1 and 3, Marigold will likely partner exclusively with women in the near future, because that's how lesbianism works.
6. INFERENCE: From 2, Hannelore will probably become a lesbian, because she's just a wildcat deep down.
7. INFERENCE: From 4, 5, and 6, Hannelore and Marigold will be thinking about sex while watching sex between men (despite having been turned off from men) to the point that their mutual induced lesbianism will be turned upon one another.
8. CONCLUSION: LESBIAN SEX!
Really, in that anime club, did you think it turned into a huge orgy every time the Inevitable Fangirl Posse was left alone?
Okay, let's start with "Hannelore is also not likely to put her face I'm-ending-this-sentence-here-kthnxbai," and "given her taste in manga, she's clearly not that creeped out by semen" (even freaking Gravitation has pile-of-tissues sight gags). Even ignoring that, there's the simple fact that these are not adolescent boys, much less the (admittedly well-grounded) stereotype of adolescent boys you're describing. It's not unreasonable to think they plan to watch this without anything steamy happening. Marigold does, as I've said, seem to have something for Hannelore, but really, it's not that impossible it could just be anxiety. And there is no reason whatsoever to think Hannelore would reciprocate. So keep in mind - this condescending is coming from a semi-shipper!
This seems like a very deniable undeniable reality, really.